#60819 yamllint gitlabci

What does this MR do?

This merge request adds yamllint (https://yamllint.readthedocs.io) compliance to the ./gitlab directory (and therefore all of the running of .gitlab-ci.yml inside the project.

I have added a custom .yamllint to the project root to make it easier to running yamllint whilst ignoring some aspects of the standards, this could be extended as required for the coding-style of the project with regards to yaml.

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry
• Code review guidelines
• Merge request performance guidelines
• Style guides

Performance and testing

• Review and add/update tests for this feature/bug. Consider all test levels. See the Test Planning Process.