feat: Implement Github CLI "pr merge" command

[Shmarkus]

Implemented gh pr merge with the possibility to define the branch or additional parameters

[KyleTryon]

Thank you for reminding me the CHANGELOG is still present here. Happy to take the change here, but we no longer user the changelog. I'll be sure to remove it in a change soon. We now use GitHub's Releases API.

https://github.com/CircleCI-Public/github-cli-orb/releases

When we publish this change, we will use this PR to populate the release notes. I'll be sure to update all that documentation. Thank you.

The code looks good. Could I ask how you intend to use this @Shmarkus ? Is there an example of config you could provide on how you plan to execute this?

By default CircleCI will trigger on a Push (including a Tag), we can augment this a bit more with https://github.com/CircleCI-Public/trigger-circleci-pipeline-action

In what scenario would you run this job?

[Shmarkus]

I can create a concrete example as well but since I'm not at the computer at the moment, I'll just illustrate my use-case.

At the moment, the Dependabot is configured to check for version updates. It creates a pull request with the new version. (Renovate bot has the same functionality)

When the test pipeline succeeds I want to merge the PR automatically (this is where the pain is at the moment)

[Shmarkus]

Added example, removed changelog from changelog

[KyleTryon]

Looks excellent and the example is a great/creative use-case, thank you!