Add band ID to list frequency plans RPC

[cvetkovski98]

Summary

Closes #6686

Changes

• Added band_id to the FrequencyPlanDescription message
• Added optional band_id to the ListFrequencyPlansRequest to enable filtering

Testing

• Updated existing unit test to ensure the fields are populated accordingly

Notes for Reviewers

• Added the band_id to the request as well to aid for the dropdown proposed in Allow users to set multiple frequency plans only in the same band #6644. This is not part of the issue description and I will remove it if not necessary.

Checklist

• Scope: The referenced issue is addressed, there are no unrelated changes.
• Compatibility: The changes are backwards compatible with existing API, storage, configuration and CLI, according to the compatibility commitments in README.md for the chosen target branch.
• Documentation: Relevant documentation is added or updated.
• The steps/process to test this feature are clearly explained including testing for regressions.
• Changelog: Significant features, behavior changes, deprecations and fixes are added to CHANGELOG.md.
• Commits: Commit messages follow guidelines in CONTRIBUTING.md, there are no fixup commits left.

[KrishnaIyer]

Very nice.