remove optional affiliation startdate from orcid validation

[floriangantner]

References

Add references/links to any related issues or PRs. These may include:

• Fixes Orcid affiliation validation checks optional start-date field as required #363
• Related to DSpace/RestContract#pr-number (if a corresponding REST Contract PR exists)

Description

see issue for more details

Instructions for Reviewers

List of changes in this PR:

• remove validation of affiliation startdate. This is not necessary in the orcid scheme
• adopt tests

Include guidance for how to test or review your PR.

• create some affiliation without startdate and push to orcid
• or check the orcid api scheme

Checklist

• My PR is small in size (e.g. less than 1,000 lines of code, not including comments & integration tests). Exceptions may be made if previously agreed upon.
• My PR passes Checkstyle validation based on the Code Style Guide.
• My PR includes Javadoc for all new (or modified) public methods and classes. It also includes Javadoc for large or complex private methods.
• My PR passes all tests and includes new/updated Unit or Integration Tests based on the Code Testing Guide.
• If my PR includes new libraries/dependencies (in any pom.xml), I've made sure their licenses align with the DSpace BSD License based on the Licensing of Contributions documentation.
• If my PR modifies REST API endpoints, I've opened a separate REST Contract PR related to this change.
• If my PR includes new configurations, I've provided basic technical documentation in the PR itself.
• If my PR fixes an issue ticket, I've linked them together.

[floriangantner]

aligned to 2023.02.02 Release