Handle followup comments and update an existing PR

[guymguym]

Need to define how this works exactly, but the idea is that after the initial issue creation, the user can post comments (to the issue or the PR or both) and make further changes to the PR.

[RobotSail]

Thinking about the possible operations we could perform here, a user could do one of:

• renaming file
• modifying a single line
  • modifying multiple lines would just be applying this operation multiple times (we could add an operator for this)
• asking for a file to regenerated
  • regenerating multiple files could just be applying this operation multiple times (again, an operator can be used to do this in one comment)

Modifying lines would just be a matter of commenting on that line with the changes you would like to make. Sometimes you can make suggestions, but this feature isn't generally available to public users, so we can ignore it for now.
Multiple lines could be altered with a comment like:

---

l50:70:

kind: UpdatedResource
metadata:
  name: "i want to use this name instead"
  namespace: "other namespace"

---

The above would signal to copilot-ops / copilot-ops-bot that the text between line 50 and 70 should be replaced with the contents in between the --- (the --- characters themselves won't be part of the comment, I'm just using those since GitHub won't let me escape backticks within code blocks).

Once we finish making edits, we'll simply stage changes for the affected files & commit back into the PR.