Tag and Note Release workflow improvements

[ArielDemarco]

Overview

This PR improves the Tag & Note Release workflow to make it more robust and readable.

Changes

• Add a per-PR concurrency group to avoid overlapping runs for the same PR number and to cancel stale executions
• Ensure the workflow only runs when a PR is merged into main and the head branch follows release/x.y.z when the workflow begins. Previously, this was a step inside the job that would mark the whole job as a fail. Now they simply won’t run.
• Extract version number directly from the branch name (kept as before, but now centralized/explicit in one step).
• Check if a tag already exists before creating a new one, and skip CocoaPods publishing if the version is already on trunk. This makes the workflow idempotent: if a run fails (e.g. during pod trunk push), re running won't re tag or re release, but will retry CocoaPods publishing.
• Simplify job structure by splitting into two clear responsibilities: tag handles tagging (necessary for SPM) and release creation, while cocoapods only pushes pods. This makes the workflow more readable and maintainable.