Add multiple frequency plans to SX1301 config file

[cvetkovski98]

Summary

Closes #6652

Changes

• Iterate through all the frequency plans when generating the global_conf.json file.

Testing

• Manual
• Add multiple frequency plans to a gateway
• Download the global_conf.json file for the gateway and ensure there is an sx1301 config entry for every frequency plan.
• Ensure that the sx1301 field in the global_conf.json file is an array when multiple frequency plans are configured and an object otherwise.

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]

The code looks good. We need to test this with some gateways though. We'll get back to you on this.

[KrishnaIyer]

Moving this to v3.28.2

[KrishnaIyer]

• For a single gateway, the generated JSON is identical to the current output.
• For multiple gateways, @adriansmares tested with a 16ch gateway and it looks like the gateway reconnected and is working.