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/lookup_plugins/test_docker_cards.py

@@ -23,7 +23,6 @@ class TestDockerCardsLookup(unittest.TestCase):
         os.makedirs(os.path.join(self.role_dir, "meta"))
         os.makedirs(os.path.join(self.role_dir, "vars"))
 
-        # Create vars/main.yml so get_application_id() can find the application_id.
         vars_main = os.path.join(self.role_dir, "vars", "main.yml")
         with open(vars_main, "w", encoding="utf-8") as f:
             f.write("application_id: portfolio\n")