Implement filter checks: ensure all defined filters are used and remove dead code

Integration tests added/updated:
- tests/integration/test_filters_usage.py: AST-based detection of filter definitions (FilterModule.filters), robust Jinja detection ({{ ... }}, {% ... %}, {% filter ... %}), plus Python call tracking; fails if a filter is used only under tests/.
- tests/integration/test_filters_are_defined.py: inverse check — every filter used in .yml/.yaml/.j2/.jinja2/.tmpl must be defined locally. Scans only inside Jinja blocks and ignores pipes inside strings (e.g., lookup('pipe', "... | grep ... | awk ...")) to avoid false positives like trusted_hosts, woff/woff2, etc.

Bug fixes & robustness:
- Build regexes without %-string formatting to avoid ValueError from literal '%' in Jinja tags.
- Strip quoted strings in usage analysis so sed/grep/awk pipes are not miscounted as filters.
- Prevent self-matches in the defining file.

Cleanup / removal of dead code:
- Removed unused filter plugins and related unit tests:
  * filter_plugins/alias_domains_map.py
  * filter_plugins/get_application_id.py
  * filter_plugins/load_configuration.py
  * filter_plugins/safe.py
  * filter_plugins/safe_join.py
  * roles/svc-db-openldap/filter_plugins/build_ldap_nested_group_entries.py
  * roles/sys-ctl-bkp-docker-2-loc/filter_plugins/dict_to_cli_args.py
  * corresponding tests under tests/unit/*
- roles/svc-db-postgres/filter_plugins/split_postgres_connections.py: dropped no-longer-needed list_postgres_roles API; adjusted tests.

Misc:
- sys-stk-front-proxy/defaults/main.yml: clarified valid vhost_flavour values (comma-separated).

Ref: https://chatgpt.com/share/68b56bac-c4f8-800f-aeef-6708dbb44199

tests/unit/roles/svc-db-postgres/filter_plugins/test_split_postgres_connections.py

@@ -77,12 +77,6 @@ class SplitPostgresConnectionsTests(unittest.TestCase):
     def test_registry_contains_filters(self):
         registry = self.mod.FilterModule().filters()
         self.assertIn("split_postgres_connections", registry)
-        self.assertIn("list_postgres_roles", registry)
-
-    def test_list_postgres_roles(self):
-        roles = self.mod.list_postgres_roles(self.roles_dir)
-        self.assertIsInstance(roles, list)
-        self.assertSetEqual(set(roles), {"app_a", "app_b"})
 
     def test_split_postgres_connections_division(self):
         # There are 2 postgres roles -> 200 / 2 = 100