Add confirmation steps to risky write commands

[ampinsk]

Right now, we have a few commands that we should ask the user to confirm before proceeding when using in a terminal.

• gh pr create (when creating fork)
• gh repo create
• gh pr merge
• gh repo fork (?)

A first pass at design:

Let me know if there are other commands that we should include here!

[vilmibm]

thanks for opening this!

[ShubhankarKG]

#1357 has a fix for gh repo create and gh pr merge. It'll be better if someone else can take up the other two commands, viz. gh pr create and gh repo fork

[AliabbasMerchant]

Great! I will take up the other two.