Add "Dry run" mode to Cherry Picking script

[getdave]

What?

Adds ability to run the Cherry Picking script in a "dry run" mode.

Part of #59399

Why?

It's all too easy to run the Cherry Picking script and have the results propagate to Github. With this flag you can run the script and be sure results will never get propagated.

This is useful when testing locally and for folks getting familiar with the workflow/tooling around releases.

How?

• Adds --dry-run flag
• Conditionalise behaviour to not propagate results if flag is provided
• Update comments output to reflect flag.

Testing Instructions

In a terminal run:

npm run other:cherry-pick -- --dry-run

• See that script will output necessary warnings
• Check the default Backport to WP RC/Beta is used as the "label" to search for and it doesn't accidentally use "--dry-run" as the label if no custom label is provided.

Testing Instructions for Keyboard

Screenshots or screencast

[getdave]

I just realised there may be a problem where --dry-run might be taken to be the label argument 🤦

[github-actions]

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Co-authored-by: getdave <get_dave@git.wordpress.org>
Co-authored-by: draganescu <andraganescu@git.wordpress.org>

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[draganescu]

Isn't this option identical to saying n at the final do you want to proceed prompt? If so, then maybe we should prompt at the start:

Choose how to run the script:
- [D]ry run, save the cherry picked branch on your computer
- [L]ive run, publish the cherry picked branch results to GitHub (this removes the labels for the cherry picked PRs too)
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