Issue #3443857 by DYdave: Automated testing on GitLab CI: Added initial...

https://www.drupal.org/project/collapse_text/issues/3443857

Automated testing on GitLab CI:

• Added initial configuration file .gitlab-ci.yml based on template and documentation from Drupal.org documentation: GitLab CI, to provide automated testing with GitLab CI pipelines.
• Fixed job cspell errors by ignoring code keywords and user names.
• Fixed job phpstan issue by implementing dependency injection in filter plugin.

For job phpcs errors, see MR !4 (merged) and issue #3427984.