fix(asm): add missing track tag to custom events tracking [backport #5365 to 1.9] (#5372)

Backport to 1.9 of #5365.

The `track_custom_event()` function was not setting the
`appsec.events.<event name>.track` tag, which is required for the event
tracking SDK. This PR fixes this.

Signed-off-by: Juanjo Alvarez <[email protected]>
(cherry picked from commit aced65e)

## Checklist

- [X] Change(s) are motivated and described in the PR description.
- [X] Testing strategy is described if automated tests are not included
in the PR.
- [X] Risk is outlined (performance impact, potential for breakage,
maintainability, etc).
- [X] Change is maintainable (easy to change, telemetry, documentation).
- [X] [Library release note
guidelines](https://ddtrace.readthedocs.io/en/stable/contributing.html#Release-Note-Guidelines)
are followed.
- [X] Documentation is included (in-code, generated user docs, [public
corp docs](https://github.com/DataDog/documentation/)).
- [X] Author is aware of the performance implications of this PR as
reported in the benchmarks PR comment.

## Reviewer Checklist

- [x] Title is accurate.
- [x] No unnecessary changes are introduced.
- [x] Description motivates each change.
- [x] Avoids breaking
[API](https://ddtrace.readthedocs.io/en/stable/versioning.html#interfaces)
changes unless absolutely necessary.
- [x] Testing strategy adequately addresses listed risk(s).
- [x] Change is maintainable (easy to change, telemetry, documentation).
- [x] Release note makes sense to a user of the library.
- [x] Reviewer is aware of, and discussed the performance implications
of this PR as reported in the benchmarks PR comment.

Author: juanjux

ddtrace/appsec/trace_utils.py

@@ -118,6 +118,8 @@ def track_custom_event(tracer, event_name, metadata):
         )
         return
 
+    span.set_tag_str("%s.%s.track" % (APPSEC.CUSTOM_EVENT_PREFIX, event_name), "true")
+
     for k, v in six.iteritems(metadata):
         span.set_tag_str("%s.%s.%s" % (APPSEC.CUSTOM_EVENT_PREFIX, event_name, k), str(v))
         span.set_tag_str(constants.MANUAL_KEEP_KEY, "true")

releasenotes/notes/asm-missing-tag-custom-events-b4d4087a2a3ce660.yaml

@@ -0,0 +1,4 @@
+---
+fixes:
+  - |
+    ASM: make ``track_custom_event()`` also set ``appsec.events.<custom_event>.track`` which was missing.

tests/appsec/test_appsec_trace_utils.py

@@ -99,3 +99,4 @@ def test_custom_event(self):
             root_span = self.tracer.current_root_span()
 
             assert root_span.get_tag("%s.%s.foo" % (APPSEC.CUSTOM_EVENT_PREFIX, event)) == "bar"
+            assert root_span.get_tag("%s.%s.track" % (APPSEC.CUSTOM_EVENT_PREFIX, event)) == "true"