[Postgres] Remove incorrect empty_default_hostname warning (DataDog#23082)

* [Postgres] Hide empty_default_hostname and remove incorrect warning

The Postgres check uses `exclude_hostname` instead of `empty_default_hostname`
for hostname exclusion. However, `empty_default_hostname` was still documented
in the example config (inherited from the global template) and the Cluster Agent
injects it unconditionally on all cluster checks, causing a confusing warning.

This change:
- Hides `empty_default_hostname` from the Postgres conf.yaml.example
- Removes the warning that fired when the option was set
- Removes the associated test

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

* Restore empty_default_hostname in EXPECTED_DEFAULTS

The field still exists in InstanceConfig (hidden only affects the
example file), so the defaults test requires it.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

* Fix changelog entry PR number

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

* Fix conf.yaml.example: hand-edit removal, restore models to master

The old local ddev (v14.0.1) was generating a different format than CI
expects. Instead, start from master's conf.yaml.example and only remove
the empty_default_hostname block. Restore config models to master state
since they should not change for this PR.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

* Simplify PR: only remove the warning, keep empty_default_hostname in config

The option is not completely unused — revert spec.yaml, conf.yaml.example,
and model changes. Only remove the warning in config.py and its test.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

* Remove accidentally staged unrelated file

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

* Update changelog wording

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

---------

Co-authored-by: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: pierreln-dd

postgres/changelog.d/23082.fixed

@@ -0,0 +1 @@
+Remove `empty_default_hostname` warning. The Cluster Agent injects this option unconditionally on cluster checks, causing a confusing warning that customers cannot prevent.

postgres/datadog_checks/postgres/config.py

@@ -390,12 +390,6 @@ def validate_config(config: InstanceConfig, instance: dict, validation_result: V
             '"dbname" parameter must be set OR autodiscovery must be enabled when using the "relations" parameter.'
         )
 
-    if config.empty_default_hostname:
-        validation_result.add_warning(
-            'The `empty_default_hostname` option has no effect in the Postgres check. '
-            'Use the `exclude_hostname` option instead.'
-        )
-
     # Validate dbname is not excluded when using autodiscovery
     # Only validate when dbname was NOT explicitly set by the user (auto-defaulted)
     # If user explicitly set dbname, they may intentionally want to connect to an excluded database

postgres/tests/test_config.py

@@ -153,15 +153,6 @@ def test_initialize_deprecated_options_warn(mock_check, minimal_instance):
     assert any("deprecated" in w for w in result.warnings)
 
 
-def test_initialize_empty_default_hostname_warns(mock_check, minimal_instance):
-    instance = minimal_instance
-    instance['empty_default_hostname'] = True
-    mock_check.instance = instance
-    mock_check.init_config = {}
-    config, result = build_config(check=mock_check)
-    assert any("empty_default_hostname" in w for w in result.warnings)
-
-
 @pytest.mark.parametrize(
     'instance, init_config, should_propagate',
     [