Example: Confirmation bubbletea-Widget with custom key map

[kalensk]

Adds another concrete bubbletea widget example on how to use the confirmation prompt with custom keyMap.

Feel free to "not" merge and close this PR since the example is so similar to the existing selection bubbletea example. It might not be needed/useful. I'll leave it to you.

[erikgeiser]

Thank you for your contribution and sorry for the late reply. I think I'll keep the examples as they are, because I'd like to have minimal examples for the basic use-cases that can easily be found. I think that the docs should be the primary way to learn about customization.

That said, I like your example and I think I'll leave this PR open for a while such that it an be easily found when someone is looking for this use-case.