Add a new release workflow

[SamMorrowDrums]

• Updates advice to contributors to merge PRs to next branch
• Adds automation to complain about merging to main.
• Adds a release publishing workflow

[github-actions]

👋 Hi there!

It looks like this PR is targeting the main branch. To help maintain our development workflow, please change the base reference to next instead.

You can change this by:

1. Clicking the "Edit" button next to the PR title
2. Changing the base branch from main to next
3. Clicking "Update pull request"

Thanks for your contribution! 🚀

[Copilot]

Pull Request Overview

This PR introduces a structured release workflow, enforces targeting the next branch for contributions, and extends Docker publishing triggers.

• Updated contributing guidelines to direct PRs to the next branch.
• Added a workflow to block PRs against main and prompt authors to switch to next.
• Introduced a manual release workflow (.github/workflows/release.yml) for tag validation, rebasing, tagging, PR creation, and a summary.
• Extended docker-publish.yml to run on both main and next branches.

Reviewed Changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated no comments.

File	Description
CONTRIBUTING.md	Added admonition and updated PR submission step to target next.
.github/workflows/release.yml	New release workflow for validating inputs, rebasing, tagging, PR creation, and summary.
.github/workflows/pr-base-check.yml	Workflow to comment on PRs targeting main, asking to switch to next.
.github/workflows/docker-publish.yml	Extended Docker publish triggers to include the next branch.

Comments suppressed due to low confidence (2)

.github/workflows/release.yml:68

• After successfully rebasing next onto main, the workflow never pushes the updated next branch back to the remote. Add a git push --force-with-lease origin next step to ensure the PR includes the rebased commits.

            echo "rebase-success=true" >> $GITHUB_OUTPUT

.github/workflows/release.yml:134

• The workflow waits for a draft release to appear but never creates one. Introduce a step (e.g., gh release create --draft "$TAG") or use an official action to generate the draft release after tagging.

          echo "Waiting for GitHub to create the draft release..."