Support for config & statistics routes

[rwxd]

This PR adds support for the /api/v1/servers/<server_id>/config & /api/v1/servers/<server_id>/statistics routes of the powerdns api.

Closes #207

[Copilot]

Pull request overview

Adds support in the proxy for PowerDNS “config” and “statistics” endpoints, controlled by new environment-level permissions.

Changes:

• Implement /api/v1/servers/{server_id}/config, /api/v1/servers/{server_id}/config/{config_setting_name}, and /api/v1/servers/{server_id}/statistics proxy routes with permission checks.
• Extend environment configuration model with global_config and global_statistics flags, plus corresponding helper checks and unit tests.
• Document the new permission flags in the README and update auth-route coverage tests to include the new endpoints.

Reviewed changes

Copilot reviewed 6 out of 6 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
powerdns_api_proxy/proxy.py	Adds the new config/statistics routes and permission gating before forwarding to upstream PowerDNS.
powerdns_api_proxy/models.py	Adds new environment flags used to authorize config/statistics access.
powerdns_api_proxy/config.py	Adds helper functions to evaluate the new environment flags.
tests/unit/proxy_test.py	Includes the new endpoints in the “missing/wrong token” route matrix.
tests/unit/config_test.py	Adds unit tests for the new global_config / global_statistics checks.
README.md	Documents the new environment options for config and statistics access.

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