Add composer.json with basic GitLab-CI and GitHub Actions

Add composer.json, following best practices for TYPO3 Projects.
Add GitLab-CI and GitHub Actions,
to ensure composer.json is valid and install is possible.

Relates: #5, #6
2 jobs for feature/5-add-composer-json in 1 minute and 30 seconds
Status Name Job ID Coverage
  Lint
passed lint:composer #19417

00:00:13

 
  Setup
passed setup:composer #19418

00:01:17