Add publishing workflows for next (unreleased) and released documentation

Notable features:
- Merges are blocked by strict Hugo reference checking. However, this
only works for references that resolve within the repository. Once you
have Hugo references to website pages beyond this repository, you will
want to remove this test job.
- Pushes to main are automatically published to "next" documentation
consistent with our other OSS projects.
- Pushes of release tags publish to a versioned directory in the
website. The website uses `v<MAJOR>.<MINOR>.x` versioning and the
"Determine technical documentation version" step will make sure that a
tag such as `v0.20.7` is mapped to `v0.20.x`.
- Pushes to release branches will only be published if there is an
existing corresponding release tag. For example, pushing to a new
release branch `release-0.1000` will not trigger a publish of
documentation until there is a `v0.1000.0` release tag.

> **Note:** I have used a release branch naming convention
`release-<MAJOR>-<MINOR>` which is consistent with grafana/mimir but I
see that in the old amixr repository there are long lived release
branches for patch versions. If that is required. I can update this PR
to support that but I would recommend not including patch versions in
release branch naming unless you have a good reason to do so.

Signed-off-by: Jack Baldry <jack.baldry@grafana.com>

.github/workflows/publish-technical-documentation-next.yml

@@ -0,0 +1,42 @@
+name: "publish-technical-documentation-next"
+
+on:
+  push:
+    branches:
+      - "main"
+    paths:
+      - "docs/sources/**"
+  workflow_dispatch:
+jobs:
+  test:
+    runs-on: "ubuntu-latest"
+    steps:
+      - name: "Check out code"
+        uses: "actions/checkout@v3"
+      - name: "Build website"
+        # -e HUGO_REFLINKSERRORLEVEL=ERROR prevents merging broken refs with the downside
+        # that no refs to external content can be used as these refs will not resolve in the
+        # docs-base image.
+        run: |
+          docker run -v ${PWD}/docs/sources:/hugo/content/docs/oncall/latest -e HUGO_REFLINKSERRORLEVEL=ERROR --rm grafana/docs-base:latest /bin/bash -c 'make hugo'
+
+  sync:
+    runs-on: "ubuntu-latest"
+    needs: "test"
+    steps:
+      - name: "Check out code"
+        uses: "actions/checkout@v3"
+
+      - name: "Clone website-sync Action"
+        run: "git clone --single-branch --no-tags --depth 1 -b master https://grafanabot:${{ secrets.GH_BOT_ACCESS_TOKEN }}@github.com/grafana/website-sync ./.github/actions/website-sync"
+
+      - name: "Publish to website repository (next)"
+        uses: "./.github/actions/website-sync"
+        id: "publish-next"
+        with:
+          repository: "grafana/website"
+          branch: "master"
+          host: "github.com"
+          github_pat: "${{ secrets.GH_BOT_ACCESS_TOKEN }}"
+          source_folder: "docs/sources"
+          target_folder: "content/docs/oncall/next"

.github/workflows/publish-technical-documentation-release.yml

@@ -0,0 +1,74 @@
+name: "publish-technical-documentation-release"
+
+on:
+  push:
+    branches:
+      - "release-*"
+    tags:
+      - "v[0-9]+.[0-9]+.[0-9]+"
+    paths:
+      - "docs/sources/**"
+  workflow_dispatch:
+jobs:
+  test:
+    runs-on: "ubuntu-latest"
+    steps:
+      - name: "Check out code"
+        uses: "actions/checkout@v3"
+      - name:
+          "Build website"
+          # -e HUGO_REFLINKSERRORLEVEL=ERROR prevents merging broken refs with the downside
+          # that no refs to external content can be used as these refs will not resolve in the
+          # docs-base image.
+        run: |
+          docker run -v ${PWD}/docs/sources:/hugo/content/docs/mimir/latest -e HUGO_REFLINKSERRORLEVEL=ERROR --rm grafana/docs-base:latest /bin/bash -c 'make hugo'
+
+  sync:
+    runs-on: "ubuntu-latest"
+    needs: "test"
+    steps:
+      - name: "Checkout code and tags"
+        uses: "actions/checkout@v3"
+        with:
+          fetch-depth: 0
+
+      - name: "Checkout Actions library"
+        uses: "actions/checkout@v3"
+        with:
+          repository: "grafana/grafana-github-actions"
+          path: "./actions"
+
+      - name: "Install Actions from library"
+        run: "npm install --production --prefix ./actions"
+
+      - name: "Determine if there is a matching release tag"
+        id: "has-matching-release-tag"
+        uses: "./actions/has-matching-release-tag"
+        with:
+          ref_name: "${{ github.ref_name }}"
+          release_tag_regexp: "^v(0|[1-9]\\d*)\\.(0|[1-9]\\d*)\\.(0|[1-9]\\d*)$"
+          release_branch_regexp: "^release-(0|[1-9]\\d*)\\.(0|[1-9]\\d*)$"
+
+      - name: "Determine technical documentation version"
+        if: "steps.has-matching-release-tag.outputs.bool == 'true'"
+        uses: "./actions/docs-target"
+        id: "target"
+        with:
+          ref_name: "${{ github.ref_name }}"
+
+      - name: "Clone website-sync Action"
+        if: "steps.has-matching-release-tag.outputs.bool == 'true'"
+        run: "git clone --single-branch --no-tags --depth 1 -b master https://grafanabot:${{ secrets.GH_BOT_ACCESS_TOKEN }}@github.com/grafana/website-sync ./.github/actions/website-sync"
+
+      - name: "Publish to website repository (release)"
+        if: "steps.has-matching-release-tag.outputs.bool == 'true'"
+        uses: "./.github/actions/website-sync"
+        id: "publish-release"
+        with:
+          repository: "grafana/website"
+          branch: "master"
+          host: "github.com"
+          github_pat: "${{ secrets.GH_BOT_ACCESS_TOKEN }}"
+          source_folder: "docs/sources"
+          # Append ".x" to target to produce a v<major>.<minor>.x directory.
+          target_folder: "content/docs/oncall/${{ steps.target.outputs.target }}.x"