XLSXConverter paths validation

Summary

Added a method that checks all paths in a worksheet for completeness and presence in the schema, called from __init__.
Addresses https://gitlab.indiscale.com/caosdb/customers/dimr/management/-/issues/261.

Focus

• Are there any path errors not included in the tests?
• Are there valid paths that trigger an error?
• Are errors and warnings used for the correct categories?

Test Environment

A test is provided, easiest way of testing is likely to modify it.

Check List for the Author

• All automated tests pass
• Reference related issues
• Up-to-date CHANGELOG.md (or not necessary)
• Up-to-date JSON schema (or not necessary)
• Appropriate user and developer documentation (or not necessary)
• Annotations in code (Gitlab comments)

Check List for the Reviewer

• I understand the intent of this MR
• All automated tests pass
• Up-to-date CHANGELOG.md (or not necessary)
• Appropriate user and developer documentation (or not necessary)
• 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 specifications? Are they satisfied?