Jinja2 template helper filter b64decode (#3242)

# What this PR does
Add an additional jinja2 template helper filter to decode base64-encoded
strings.

An example of an incoming integration payload that would benefit from
this filter is GCP's pubsub message:

https://cloud.google.com/pubsub/docs/reference/rest/v1/PubsubMessage 

## Which issue(s) this PR fixes

## Checklist

- [x] Unit, integration, and e2e (if applicable) tests updated
- [x] Documentation added (or `pr:no public docs` PR label added if not
required)
- [ ] `CHANGELOG.md` updated (or `pr:no changelog` PR label added if not
required)

---------

Co-authored-by: Jorge Vargas <jorge.vargas@homeprotech.com>
Co-authored-by: Joey Orlando <joey.orlando@grafana.com>
Co-authored-by: Joey Orlando <joseph.t.orlando@gmail.com>

CHANGELOG.md

@@ -7,6 +7,10 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## Unreleased
 
+### Added
+
+- Add `b64decode` Jinja2 template helper filter by @jorgeav ([#3242](https://github.com/grafana/oncall/pull/3242))
+
 ## v1.3.53 (2023-11-03)
 
 ### Fixed

docs/sources/jinja2-templating/_index.md

@@ -206,5 +206,6 @@ Built-in functions:
 - `datetimeformat` - converts time from datetime to the given format (`%H:%M / %d-%m-%Y` by default)
 - `regex_replace` - performs a regex find and replace
 - `regex_match` - performs a regex match, returns `True` or `False`. Usage example: `{{ payload.ruleName | regex_match(".*") }}`
+- `b64decode` - performs a base64 string decode. Usage example: `{{ payload.data | b64decode }}`
 
 {{< section >}}

engine/common/jinja_templater/filters.py

@@ -1,3 +1,4 @@
+import base64
 import json
 import re
 
@@ -51,3 +52,10 @@ def json_dumps(value):
         return json.dumps(value)
     except (ValueError, AttributeError, TypeError):
         return None
+
+
+def b64decode(value):
+    try:
+        return base64.b64decode(value).decode("utf-8")
+    except (ValueError, AttributeError, TypeError):
+        return None

engine/common/jinja_templater/jinja_template_env.py

@@ -4,6 +4,7 @@ from jinja2.exceptions import SecurityError
 from jinja2.sandbox import SandboxedEnvironment
 
 from .filters import (
+    b64decode,
     datetimeformat,
     iso8601_to_time,
     json_dumps,
@@ -29,3 +30,4 @@ jinja_template_env.filters["regex_replace"] = regex_replace
 jinja_template_env.filters["regex_match"] = regex_match
 jinja_template_env.filters["regex_search"] = regex_search
 jinja_template_env.filters["json_dumps"] = json_dumps
+jinja_template_env.filters["b64decode"] = b64decode

engine/common/tests/test_base64decode.py

@@ -0,0 +1,7 @@
+from common.jinja_templater.filters import b64decode
+
+
+def test_base64_decode():
+    original = "dGVzdCBzdHJpbmch"
+    expected = "test string!"
+    assert b64decode(original) == expected

grafana-plugin/src/components/CheatSheet/CheatSheet.config.ts

@@ -83,6 +83,7 @@ export const genericTemplateCheatSheet: CheatSheetInterface = {
         { listItemName: 'time(), datetimeformat, iso8601_to_time' },
         { listItemName: 'to_pretty_json' },
         { listItemName: 'regex_replace, regex_match' },
+        { listItemName: 'b64decode' },
       ],
     },
     {