[FEAT]: Support "Copilot Code Review" repo settings

### Describe the need

The "Copilot > Code review" repository settings don't appear to have a way to configure them in this TF provider. I was informed about Copilot's new "Review effort level" setting yesterday, and would love for our teams to be able to manipulate this setting for their repos.

It looks like the current options are "Low" and "Medium" but there is a "High" option "coming soon".

For our particular use case right now, we don't require support for modifying "Use custom instructions when reviewing pull requests" or "Allow Copilot to use MCP tools when reviewing pull requests" but if those are all kind of together with the GitHub API then perhaps it makes sense to go ahead and support them all at the same time.

### GitHub Installation Type

- [ ] GitHub.com (Free, Pro, or Team)
- [ ] GitHub Enterprise Server (on-premises)
- [ ] GitHub Enterprise Cloud with Personal Accounts (github.com)
- [ ] GitHub Enterprise Cloud with Managed Users/EMU (github.com)
- [ ] GitHub Enterprise Cloud with Data Residency (*.ghe.com)
- [ ] I don't know

### Relevant log output

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### Code of Conduct

- [x] I agree to follow this project's Code of Conduct