feat: add support for custom REST handlers without UI in web.conf and restmap.conf

[kkedziak-splunk]

Issue number: ADDON-75952

PR Type

What kind of change does this PR introduce?

• Feature
• Bug Fix
• Refactoring (no functional or API changes)
• Documentation Update
• Maintenance (dependency updates, CI, etc.)

Summary

Changes

Second PR. It allows to specify REST handlers not generated by UCC in globalConfig. Based on that, UCC will extend openapi.json, web.conf and restmap.conf.

User experience

Nothing changes in existing addons. This feature introduces new options in global config.

Checklist

If an item doesn't apply to your changes, leave it unchecked.

• I have performed a self-review of this change according to the development guidelines
• Tests have been added/modified to cover the changes (testing doc)
• Changes are documented
• PR title and description follows the contributing principles

[kkedziak-splunk]

Suggested pull request title: feat: allow definition of custom REST handlers in global config

I appreciate the thorough implementation of support for custom REST handlers in the global configuration. The code is well-structured and includes comprehensive test coverage. The implementation follows good practices by separating concerns into appropriate classes and methods.

However, there are a few areas that could be improved:

1. The copyright year in splunk_add_on_ucc_framework/commands/rest_builder/user_defined_rest_handlers.py is set to 2025, which seems incorrect. It should probably be 2023 or 2024.

2. In user_defined_rest_handlers.py, there are some commented-out type hints in docstrings that could be cleaned up or properly documented.

3. Consider adding more detailed docstrings to the main classes (RestHandlerConfig and UserDefinedRestHandlers) explaining their purpose and usage.

4. In test_user_defined_rest_handlers.py, consider grouping related test cases using pytest.mark.parametrize to reduce code duplication, especially in the duplicates testing section.

5. The schema.json changes could benefit from more detailed descriptions in the documentation strings to help users understand the new configuration options.

Overall, the code appears to be ready for merging after addressing these minor issues. The implementation provides a useful feature for defining custom REST handlers without requiring UI components, and it's well-tested with both unit tests and integration tests.

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