Need ability to specify different github URLs

[jnurthen]

Is your feature request related to a problem? Please describe.
The ARIA suite of specifications are now in a monorepo so all PRs and commits are in a single github repository. However we still track issues in their separate repository.

As such we can't specify the github URLs correctly in the header document. What we would like is the following in the Feedback section (for core-aam for example) - is to specify the ARIA repository for the "pull requests" section

[GitHub w3c/core-aam](https://github.com/w3c/core-aam/)
([pull requests](https://github.com/w3c/aria/pulls/), 
[new issue](https://github.com/w3c/core-aam/issues/new/choose), 
[open issues](https://github.com/w3c/core-aam/issues/))

and for the commit history

[Commit history](https://github.com/w3c/aria/commits/)

For extra credit allow the PR link to include a label so the URL we would use for that would actually be
https://github.com/w3c/aria/pulls?q=is%3Aopen+is%3Apr+label%3Aspec%3Acore-aam

Describe the solution you'd like
Provide an override for the Pull Request URL/ commit history URL

Additional context
Add any other context or screenshots about the feature request here.

Describe any alternatives you've considered
We are not - I'm considering using JS in the postProcess to switch the URLs but there is no good selector to target

Can you or your organization fund the work or help with development?
Yes - I can probably create a PR if we get agreeement on an implementation.

[sidvishnoi]

This is a welcome change. Given respecConfig.github can be an object, it should be fairly straightforward to support. PR welcome.