feat: add timestamp_to_datetime jinja template filter (#5303)

Related to grafana/support-escalations#13670

Given a payload like this:

```
{  
    "Sometime": "1730893740"  
}
```

the following template expression:

`{{ payload.Sometime | int | timestamp_to_datetime }}`

will render as:

`2024-11-06 11:49:00`

docs/sources/configure/jinja2-templating/advanced-templates/index.md

@@ -94,6 +94,7 @@ Grafana OnCall enhances Jinja with additional functions:
 - `datetimeparse`: Converts string to datetime according to strftime format codes (`%H:%M / %d-%m-%Y` by default)
 - `timedeltaparse`: Converts a time range (e.g., `5s`, `2m`, `6h`, `3d`) to a timedelta that can be added to or subtracted from a datetime
   - Usage example: `{% set delta = alert.window | timedeltaparse %}{{ alert.startsAt | iso8601_to_time - delta | datetimeformat }}`
+- `timestamp_to_datetime`: Converts a Unix/Epoch time to a datetime object
 - `regex_replace`: Performs a regex find and replace
 - `regex_match`: Performs a regex match, returns `True` or `False`
   - Usage example: `{{ payload.ruleName | regex_match(".*") }}`

engine/common/jinja_templater/filters.py

@@ -30,6 +30,13 @@ def datetimeformat_as_timezone(value, format="%H:%M / %d-%m-%Y", tz="UTC"):
         return None
 
 
+def timestamp_to_datetime(value):
+    try:
+        return datetime.fromtimestamp(value)
+    except (ValueError, AttributeError, TypeError):
+        return None
+
+
 def iso8601_to_time(value):
     try:
         return parse_datetime(value)

engine/common/jinja_templater/jinja_template_env.py

@@ -15,6 +15,7 @@
     regex_replace,
     regex_search,
     timedeltaparse,
+    timestamp_to_datetime,
     to_pretty_json,
 )
 
@@ -39,3 +40,4 @@ def raise_security_exception(name):
 jinja_template_env.filters["json_dumps"] = json_dumps
 jinja_template_env.filters["b64decode"] = b64decode
 jinja_template_env.filters["parse_json"] = parse_json
+jinja_template_env.filters["timestamp_to_datetime"] = timestamp_to_datetime

engine/common/tests/test_apply_jinja_template.py

@@ -66,6 +66,17 @@ def test_apply_jinja_template_iso8601_to_time():
     assert result == expected
 
 
+def test_apply_jinja_template_timestamp_to_datetime():
+    payload = {"sometime": 1730893740}
+
+    result = apply_jinja_template(
+        "{{ payload.sometime | timestamp_to_datetime }}",
+        payload,
+    )
+    expected = str(datetime.fromtimestamp(payload["sometime"]))
+    assert result == expected
+
+
 def test_apply_jinja_template_datetimeformat():
     payload = {"aware": "2023-05-28 23:11:12+0000", "naive": "2023-05-28 23:11:12"}