query transaction filter (BEFORE/AFTER)

Summary

Fix/Enhancement of #132 (closed)

The issue was misclassified as bug, the documentation was no very helpful, apparently. Since the implementation was very straight forward, I decided to do it anyways.

Focus

The mysql backend api has not changed. Only the CQL parser (CQLParser.g4/CQLLexer.g4) and the filter implementation of the server (TransactionFilter.java) had to be extended.

Test Environment

Tests in caosdb-pyinttest!6 (merged) should be sufficient

Check List for the Author

• 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

@@ -20,6 +20,9 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
   to determine whether the server's state has changed between queries.
 * Basic caching for queries. The caching is enabled by default and can be
   controlled by the usual "cache" flag.
+* Add `BEFORE`, `AFTER`, `UNTIL`, `SINCE` keywords for query transaction
+  filters.
+
 
 ### Changed