[DBMON-5479] Add database_instance to mysql_variables event (DataDog#20620)

* Add database_instance to mysql_variables event

* add changelog

Author: eric-weaver

mysql/changelog.d/20620.fixed

@@ -0,0 +1 @@
+Fixes missing mysql variables from database instances configured with templated names

mysql/datadog_checks/mysql/metadata.py

@@ -173,6 +173,7 @@ def report_mysql_metadata(self):
             settings = [dict(row) for row in rows]
         event = {
             "host": self._check.reported_hostname,
+            "database_instance": self._check.database_identifier,
             "agent_version": datadog_agent.get_version(),
             "dbms": "mysql",
             "kind": "mysql_variables",

mysql/tests/test_metadata.py

@@ -72,6 +72,7 @@ def test_collect_mysql_settings(aggregator, dbm_instance, dd_run_check):
     event = next((e for e in dbm_metadata if e['kind'] == 'mysql_variables'), None)
     assert event is not None
     assert event['host'] == "stubbed.hostname"
+    assert event['database_instance'] == "stubbed.hostname"
     assert event['dbms'] == "mysql"
     assert len(event["metadata"]) > 0