Trigger layer version update in documentation

[rithikanarayan]

What does this PR do?

Adds Gitlab job to release pipelines to trigger DataDog/serverless-ci pipeline which will generate a PR for updating the layer version in public documentation. Then, serverless ONE will review and merge this PR.

Motivation

Keeps public facing documentation up-to-date.

Testing Guidelines

Additional Notes

Types of Changes

• Bug fix
• New feature
• Breaking change
• Misc (docs, refactoring, dependency upgrade, etc.)

Check all that apply

• This PR's description is comprehensive
• This PR contains breaking changes that are documented in the description
• This PR introduces new APIs or parameters that are documented and unlikely to change in the foreseeable future
• This PR impacts documentation, and it has been updated (or a ticket has been logged)
• This PR's changes are covered by the automated tests
• This PR collects user input/sensitive content into Datadog
• This PR passes the integration tests (ask a Datadog member to run the tests)