Added support for making branches read-only

[jefflill]

Resolves #2714

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Behavior

Before the change?

• Octokit.net doesn't currently support making branches read-only

After the change?

• I've added LockBranch properties to the various branch protection models, next to the existing EnforceAdmins properties.
• I've also published a temporary nuget with this functionality to: https://www.nuget.org/packages/Neon.Octokit/6.0.2

Other information

• The existing unit tests pass
• I didn't see any related integration unit tests in your repo, but I have verified this in unit tests for our repo using this.

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Additional info

Pull request checklist

• Tests for the changes have been added (for bug fixes / features)
  I didn't see any related integration unit tests in your repo, but I have verified this in unit tests for our repo using this.
• Docs have been reviewed and added / updated if needed (for bug fixes / features)
• Added the appropriate label for the given change

Does this introduce a breaking change?

Please see our docs on breaking changes to help!

• Yes (Please add the Type: Breaking change label)
• No

If Yes, what's the impact:

Pull request type

Please add the corresponding label for change this PR introduces:

Type: Feature

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[nickfloyd]

Thanks again for the changes. ❤️ There is just one minor modification needed before we can merge this in.

[nickfloyd]

Hey @jefflill, Thanks for this change! ❤️ . We use spaces in this project - they need to be updated in this file. Would you mind either:

1. Updating this to reflect what I mentioned above and pushing the update to this PR or...
2. Setting the fork to give maintainers write access and I'd be glad to make the change

[nickfloyd]

@jefflill, Just a gentle bump on this. Let me know if either option above works for you. Thanks again for your contributions!