pull_request: add ability to edit commit message from PR in Lando UI

[Magnolia-Liu]

• modify view to be called by GitHub to update pull request content with data from Lando
• add editable commit body and title fields
• add save commit message button which refreshes page
• add error display for invalid input

TO DO:

• improve usability eg. disable editing during save, disabling pr button while saving, changing font + textbox size, etc.
• add tests
• make error handling more robust ie. pulling errors directly from github alongside using form checks, making character limit more strict/add warnings to better align with readability standards

[github-actions]

View this pull request in Lando to land it once approved.

[zzzeid]

Just a few drive-by comments

[zzzeid]

To reduce chances of this PR getting blocked, we can take out the portions in this PR that were borrowed from #1073 and instead just keep the _patch and _patch methods. We can always re-add the delimiter functionality after that PR is more robust.

[zzzeid]

Would be good to add docstrings to this method and the class.