[Tooling] Automate Release Publishing

[iangmaia]

This PR automates the release publishing, which means to:

• Publish the existing draft release on GitHub (which will also have GitHub create the associated git tag, pointing to the tip of the branch)
• If the release branch for the next version already exists, backmerge the current release into it
• Delete the current release branch

This PR will be followed by updates to the Releases V2 tool.

[wpmobilebot]

📲 You can test the changes from this Pull Request in WordPress Alpha by scanning the QR code below to install the corresponding build.

	App Name	WordPress Alpha
	Configuration	Release-Alpha
	Build Number	pr23592-355c3d5
	Version	25.3
	Bundle ID	org.wordpress.alpha
	Commit	355c3d544a41fd1ca30221e6dc941b3fd81876eb
	App Center Build	WPiOS - One-Offs #10678

Automatticians: You can use our internal self-serve MC tool to give yourself access to App Center if needed.

[wpmobilebot]

📲 You can test the changes from this Pull Request in Jetpack Alpha by scanning the QR code below to install the corresponding build.

	App Name	Jetpack Alpha
	Configuration	Release-Alpha
	Build Number	pr23592-355c3d5
	Version	25.3
	Bundle ID	com.jetpack.alpha
	Commit	355c3d544a41fd1ca30221e6dc941b3fd81876eb
	App Center Build	jetpack-installable-builds #9722

Automatticians: You can use our internal self-serve MC tool to give yourself access to App Center if needed.