Add MACSettings.DesiredMaxEIRP field

[neoaggelos]

Summary

Closes #4090

Changes

• Introduce DeviceEIRPValue struct (containing an enum value of type DeviceEIRP)
• Introduce MACSettings.DesiredMaxEirp field.
• Consider MaxEirp value for mac.DeviceDesiredMaxEIRP
• Miscellaneous changes required for validations and setting the DesiredMaxEirp field from the CLI.

Testing

• Unit tests
• Setting desired_max_eirp field from the CLI and verify that the DesiredParameters.MaxEIRP value is set properly after device joins.

Regressions

There should not be any, the default value for the new setting is nil which preserves the old behaviour.

Notes for Reviewers

• Not using gogoproto, so the field is DesiredMaxEirp instead of DesiredMaxEIRP.
• The validation and FieldIsZero() parts probably need a review from @rvolosatovs to make sure that I did not miss anything.

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.
• 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.

[johanstokking]

LGTM

[htdvisser]

I really don't know much about how these custom wrappers work, so maybe good to wait for review from @rvolosatovs.

[adriansmares]

Nothing to add.