Allow publishing from any branch

[hsubox76]

This works in tandem with a change to the internal release-cli script (that branch is currently named custombranch).

The change to that script is, if publishing from master, the release branch is named release. If publishing from any other branch, the release branch is named [branch name]-releasebranch. I was going to make the suffix -release but I did a search and it's not uncommon to end dev branches with -release if we're working on the release process. So trying to make something more unique.

[changeset-bot]

⚠️ No Changeset found

Latest commit: e58a180

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[google-oss-bot]

Binary Size Report

Affected SDKs

No changes between base commit (4d747b1) and head commit (b68cb8a).

Test Logs

• Base (4d747b15): https://github.com/firebase/firebase-js-sdk/actions/runs/1151594647
• Head (b68cb8a8): https://github.com/firebase/firebase-js-sdk/actions/runs/1152263261

[google-oss-bot]

Size Analysis Report

Affected Products

No changes between base commit (4d747b1) and head commit (b68cb8a).

Test Logs

• Base (4d747b1): https://github.com/firebase/firebase-js-sdk/actions/runs/1151594647
• Head (b68cb8a): https://github.com/firebase/firebase-js-sdk/actions/runs/1152263261

[Feiyang1]

Nice. Didn't know that GHA provides convenient util functions.