ci: port PR template, ready-for-review label + PR-review gate workflows from ruby-sdk

[xxshubhamxx]

What is this about?

Ports the PR-hygiene tooling from browserstack-ruby-sdk into this repo, verbatim:

File	Purpose
.github/PULL_REQUEST_TEMPLATE.md	PR template with the ## Release section (version bump + internal release notes) that the ready-for-review gate reads
.github/workflows/ready-for-review-label.yml	ready-for-review label workflow — validates the ## Release section, removes the ready-for-review label when the body fails the gate, and fails the check until the label is present. Manually-applied, required merge gate.
.github/workflows/sdk-pr-review-gate.yml	PR-review check workflow (SDK PR Review Gate) — green only when the ready-for-review label is present and the SDK PR Review Agent's latest verdict marker reports state=success on the current head SHA.

Source: browserstack-ruby-sdk@23b89cb. Files copied unchanged so behaviour stays identical across SDK repos.

Related Jira task/s

• N/A (CI tooling port)

Release (mandatory for every PR — required for the ready-for-review label)

Version bump: (required — tick exactly one)

• minor (backwards-compatible feature)
• patch (bug fix or other small change)

Release notes type: (optional)

• Other Improvement

Release notes (customer-facing): (optional but encouraged)

Release notes (internal): (required — engineer-facing; what actually changed / why)

• Ported the PR template, ready-for-review label workflow, and SDK PR Review gate workflow from browserstack-ruby-sdk so PR hygiene is consistent across SDK repos.

Operational prerequisites (before these gates function)

These files are copied as-is; to make them enforce anything the repo admin still needs to:

1. Create the ready-for-review label in the repo (the workflow only ever removes it — the author applies it manually; it does not create it).
2. (Optional) add the SLACK_PR_SLA_WEBHOOK secret — without it, Slack notify steps log and skip (non-fatal).
3. Wire the SDK PR Review Agent so it posts the <!-- sdk-pr-review:verdict sha=… state=… --> marker; until then SDK PR Review Gate stays red on real PRs.
4. Update branch protection to require the check-ready and gate checks (plus "Require approvals") once the above are in place.

Until branch protection requires them, both new workflows run as informational (non-blocking) checks. This PR's own body follows the new template so the release-gate logic passes; the ready-for-review label check will still show red here until the label is applied — expected.

Checklist

• Ready to review
• Has it been tested locally?

PR Validations

Run Tests: Comment RUN_TESTS to trigger sanity tests.

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