Related to https://github.com/grafana/oncall-private/issues/2826
RBAC enabled or not (OSS or cloud), it is possible to get service
account permissions, enabling perm check (for service account tokens) in
public API.
Also allow empty value for users in sync (instead of returning a 400
response).
# What this PR does
This PR:
- adds a few attributes to paginated API responses
- removes channel filter "send demo alert" internal API endpoint + tests
(this endpoint was marked as deprecated + not consumed by the web UI)
With the new paginated API response schema, the web UI will no longer
need to:
- hardcode `ITEMS_PER_PAGE` for each table
- manually calculate total number of pages
(these two things ☝️ will be done in
https://github.com/grafana/oncall/issues/2476)
For `GET /api/internal/v1/alertgroups` the response will now look like
this:
```diff
{
"next": <url> | None,
"previous": <url> | None,
"results": [],
++ "page_size": <int>
}
```
For all other paginated API responses, the response will now look like:
```diff
{
"count": <int>,
"next": <url> | None,
"previous": <url> | None,
"results": [],
++ "page_size": <int>,
++ "current_page_number": <int>,
++ "total_pages": <int>
}
```
## TODO
- [x] update public API docs to include these new attributes
## Checklist
- [x] Unit, integration, and e2e (if applicable) tests updated
- [x] Documentation added (or `pr:no public docs` PR label added if not
required)
- [x] `CHANGELOG.md` updated (or `pr:no changelog` PR label added if not
required)
