Allow editing commit message for squash merge

[mrswats]

Allow Editing Commit message for squash merge

In the GitHub UI you are allowed to modify the commit message before you merge squash a pull request. This capability was added in the CLI: https://github.com/cli/cli/issues/1023, but I couldn't find the option to do this in Octo.

Describe what happened (or what feature you want)

I would like to be able to edit the commit message before merging.

Original question: https://github.com/pwntester/octo.nvim/discussions/264

[pwntester]

Hi! Can you describe the workflow you would like to be implemented?

1. Octo pr merge squash body (adding a body flag), a popup opens and when the window closed, the text is used for the gh --body parameter
2. Octo pr merge_edit squash (using a different action). Similar behaviour (popup -> --body)

Im leaning for the second one. Any preferences?

[mrswats]

If possible I would love for a buffer with the default text to appear always and then that text is used for the commit message. This way, we can pass a flag to act as --fill or something along these lines.

[vitorf7]

@pwntester I would probably lean towards the first one. We could however as @mrswats was saying maybe by default (or based on a configuration option) open a pop to change the commit message. We could also add the body flag as a way to get that pop up (if people have the auto change config opt turned off).