feat: Implement release and changelog process

[lornakelly]

Description

Original Spike: #109

After spike investigation, the following tool focused on monorepos wwill be a good fit: https://github.com/changesets/changesets

Motivation

Establish a simple, consistent process for delivering the package to npm, ensuring changes are tracked, versioned, and communicated clearly.

Proposed Implementation

Based on findings: use 2 GH Actions and create release branches to allow us to fix previous releases when required.

Release strategy steps

GHA: Prepare Release

• Triggered manually via workflow_dispatch.
• Creates a release branch
• Runs changesets/action without publishing.
• Updates package versions.
• Updates package-level CHANGELOG.md files.
• Creates a release PR targeting the release branch, i.e. `1.0`

Manual review and merge

•  People review the changes and merge the release PR into the release branch

GHA: Publish Release

• Automatically runs only when the release PR is merged into the official release branch.
• Check that the merged PR is a release PR by checking:
  • release branch name
  • authored by github-actions[bot] or similar
  • release-pr or similar on PR title.
• Checks out the release branch
• Runs `pnpm install` and build:prod together with the tests
• Runs changeset publish through changesets/action.
• Creates release tags through Changesets.
• Creates GitHub Releases through changesets/action.
• Publishes npm packages, ideally via npm Trusted Publishing/OIDC similarly to serverlessworkflow/sdk-typescript.

Definition of Done

• Implementation: Fully implemented according to the Serverless Workflow spec.
• Unit Tests: Comprehensive unit tests are included and passing.
• Integration Tests: Verified within the monorepo and target environments (Web/VS Code).
• Documentation: Updated README.md, ADRs, or official docs.
• Performance: No significant regression in editor responsiveness.
• Accessibility: UI changes comply with accessibility standards.