feat: add deploy to custom repo

[s00d]

Hello, I don't know why you haven't done this yet, but it's very simple and clear.

The changes allow creating a release in a separate repository, requiring the use of 4 parameters: owner, repo, GITHUB_TOKEN, and releaseCommitish.

I added the description to the readme.

[FabianLars]

Thanks for contributing!

A few things and then this will be ready to go:

• I think it's fine if you move the context.repo.owner into index.ts when the const is declared instead of falling back to null. Should hopefully make the code even cleaner
• I think the readme changes belongs into the Release Configuration block instead.
• Please run pnpm format after the changes -> I will add the missing github workflow for that check in the meantime.
• Lastly, we'll also need a changefile, similar to this one https://github.com/tauri-apps/tauri-action/blob/5eb86f2895edc041147c42d25bee9dc899de189b/.changes/artifacts-output.md?plain=1

Thanks again :)

[s00d]

@FabianLars done, thanks for the reply

[FabianLars]

Thank you!