Finalize Command Palette Spec (#5674)

## Summary of the Pull Request

This PR aims to move the command palette spec out of the draft state and into a finalized state for inclusion in the 2.0 version of the Windows Terminal. 

Notably, I've added sections regarding the ability to run `wt` commandlines using the Command Palette UI, something we hadn't considered in the original draft, because `wt` commandlines didn't land for like _4 months_ after this first draft.

## References
* #2046 - the original command palette thread
* #2193 - the original draft PR
* #5400 - the new command palette megathread for WT 2.0, which I'll be updating with follow-up tasks as we work on implementing this.

## PR Checklist
* [x] Specs #2046
* [x] I work here
* [x] Is documentation

## Detailed Description of the Pull Request / Additional comments

_read the spec_

.github/actions/spell-check/dictionary/dictionary.txt

@@ -28673,11 +28673,8 @@ attacco
 attach
 attachable
 attachableness
-attache
 attached
 attachedly
-attacher
-attachers
 attaches
 attacheship
 attaching