ci: add release-please

[venkatamutyala]

Brings codespaces onto the GlueOps-standard release-please setup, replacing the scheduled bump_version.yaml mechanism.

What changed

• Add .github/workflows/release-please.yaml — authenticates via the public-release-please GitHub App (create-github-app-token, org secrets RELEASE_PLEASE_APP_ID / RELEASE_PLEASE_APP_PRIVATE_KEY), manifest mode.
• Add release-please-config.json — release-type: simple, package-name: codespaces, include-component-in-tag: false (plain vX.Y.Z tags), full changelog-sections, and bump-minor-pre-major: true (0.x repo → breaking change bumps minor, not to 1.0.0).
• Add .release-please-manifest.json — seeded to 0.143.0 (continues from the latest tag v0.143.0).
• Remove .github/workflows/bump_version.yaml — the scheduled caller of the shared bump-version-cut-release reusable workflow. release-please replaces it; running both would create conflicting tags/releases. After this, releases cut only on feat:/fix:/breaking Conventional Commits (no longer every 2 days on cron).

Image build chain — unchanged

build_and_publish_devcontainer.yml already triggers on push: tags: ['v*'], and packer-qemu.yml chains off it via workflow_run. Because the App-token tag push (unlike GITHUB_TOKEN) triggers downstream workflows, the existing devcontainer → packer chain fires on each release tag. No changes to those workflows.

⚠️ Prerequisite to confirm (org admin)

codespaces is a public repo, so org secret RELEASE_PLEASE_APP_PRIVATE_KEY must have All repositories visibility (or Selected incl. this repo); otherwise create-github-app-token fails. I couldn't verify this (not an org admin).

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