add logic for postgres auto discovered for custom_queries

[artemsafiyulin]

What does this PR do?

This PR make possible to use custom_queries with auto discovery. Previously it doesn't work.

Motivation

This feature needs for work.

How it has been tested:

1. created couple databases:

docker exec pg-ad-test psql -U postgres -c "\l"
                                 List of databases
   Name    |  Owner   | Encoding |  Collate   |   Ctype    |   Access privileges
-----------+----------+----------+------------+------------+-----------------------
 db1       | postgres | UTF8     | en_US.utf8 | en_US.utf8 |
 db2       | postgres | UTF8     | en_US.utf8 | en_US.utf8 |
 postgres  | postgres | UTF8     | en_US.utf8 | en_US.utf8 |
 template0 | postgres | UTF8     | en_US.utf8 | en_US.utf8 | =c/postgres          +
           |          |          |            |            | postgres=CTc/postgres
 template1 | postgres | UTF8     | en_US.utf8 | en_US.utf8 | =c/postgres          +
           |          |          |            |            | postgres=CTc/postgres
(5 rows)

2. created environment using ddev (output in file start_output.txt)

3. prepare test config with custom metric and enabled autodiscovery

init_config: {}

instances:
  - host: 127.0.0.1
    port: 55432
    username: postgres
    password: postgres
    only_custom_queries: true
    database_autodiscovery:
      enabled: true
      include: [".*"]
      global_view_db: postgres
    custom_queries:
      - query: "select current_database(), 1 as dummy_metric"
        columns:
          - name: dbname
            type: tag
          - name: dummy_metric
            type: gauge

4. Run test on old code wich don't work for custom_queries with autodiscovery (results in file run-old-behavior.txt) - here you can see that metric collected only for postgres db (default db)

/usr/local/ddev/bin/ddev -x env reload postgres latest && /usr/local/ddev/bin/ddev -x env agent postgres latest check postgres

5. add changes from this PR to code

1. Current code
docker exec dd_postgres_latest bash -lc "nl -ba /opt/datadog-agent/embedded/lib/python3.13/site-packages/datadog_checks/postgres/postgres.py | sed -n '1138,1155p'"
  1138	                    self.statement_samples.run_job_loop(tags)
  1139	                    self.metadata_samples.run_job_loop(tags)
  1140	                if self._config.collect_wal_metrics:
  1141	                    # collect wal metrics for pg < 10, disabled by enabled
  1142	                    self._collect_wal_metrics()
  1143	
  1144	            if self._query_manager.queries:
  1145	                if self.autodiscovery:
  1146	                    for dbname in self.autodiscovery.get_items():
  1147	                        # run custom queries against each discovered database with the correct db tag
  1148	                        db = functools.partial(self.db_pool.get_connection, dbname=dbname)
  1149	                        autodiscovery_tags = list(self.tags_without_db) + [f"db:{dbname}"]
  1150	                        self._query_manager.executor = functools.partial(self.execute_query_raw, db=db)
  1151	                        self._query_manager.execute(extra_tags=autodiscovery_tags)
  1152	                else:
  1153	                    self._query_manager.executor = functools.partial(self.execute_query_raw, db=self.db)
  1154	                    self._query_manager.execute(extra_tags=tags)

6. run tests on new code (results in file run-new-behavior.txt) - now you can see that custom query metric collected 3 times (for default postgres db and for two auto discovered db1 and db2)

[chatgpt-codex-connector]

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[chatgpt-codex-connector]

Avoid skipping custom queries on secondary DBs

When autodiscovery is enabled, this loop reuses the same QueryManager/Query instances for every database. Query.should_execute() updates its last-execution timestamp the first time a query runs, so any custom query with collection_interval set will be skipped for the remaining databases in the same check cycle and then continue to only run for the first database on subsequent cycles. This means multi-DB setups silently lose custom query metrics for all but the first autodiscovered DB whenever collection_interval is configured. Consider creating per-database query managers or resetting per-query execution state before each DB run so the interval is enforced per database.

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[codecov]

Codecov Report

❌ Patch coverage is 25.00000% with 6 lines in your changes missing coverage. Please review.
✅ Project coverage is 89.35%. Comparing base (375fab0) to head (42bd13d).
⚠️ Report is 4 commits behind head on master.

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