chore: Add yamllint action to allowed actions

[lindnerby]

Description

It's good practice to lint everything in a repository and since we usually handle one or the other yaml file, we also want to lint yamls in the repositories of lifecycle-manager, runtime-watcher, templator-operator and modulectl.

Changes proposed in this pull request:

• Allow latest release sha version of yamllint-action
• This action uses yamllint to lint yaml files
• yamllint documentation

Related issue(s)