ENH: Introduce css classes for required form fields

Summary

In the course of https://gitlab.indiscale.com/caosdb/customers/geomar/management/-/issues/42, it was necessary to introduce additional css classes that can be styled individually.

Focus

Introduced new classes in form_elements.js and their default styling in webcaosdb.css.

Test Environment

Test with any instance that uses web forms (e.g., the demo profile) and verify that the old styling is still present with the new classes. You may use, e.g., Firefox's development tools to verify that the classes indeed can be styled.

Check List for the Author

Please, prepare your MR for a review. Be sure to write a summary and a focus and create gitlab comments for the reviewer. They should guide the reviewer through the changes, explain your changes and also point out open questions. For further good practices have a look at our review guidelines

• All automated tests pass
• Reference related Issues
• Up-to-date CHANGELOG.md
• Annotations in code (Gitlab comments)
  • Intent of new code
  • Problems with old code
  • Why this implementation?

Check List for the Reviewer

• I understand the intent of this MR
• All automated tests pass
• Up-to-date CHANGELOG.md
• The test environment setup works and the intended behavior is reproducible in the test environment
• In-code documentation and comments are up-to-date.
• Check: Are there spezifications? Are they satisfied?

For further good practices have a look at our review guidelines.

CHANGELOG.md

@@ -14,6 +14,8 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
   with the full version history of the first entity on the page.
 * `BUILD_MODULE_SHOW_ID_IN_LABEL` build variable with which the showing of
   entity ids together with their names if it is enabled (disabled by default).
+* Introduced `caosdb-f-form-required-marker` and `caosdb-f-form-required-label`
+  css classes for the markers of required fields in CaosDB form elements.
 
 ### Changed (for changes in existing functionality)