GH-4779 Maintain RDFa support

[edwardsph]

GitHub issue resolved: #4779

Briefly describe the changes proposed in this PR:

This flag is not ready for deprecation as it is used by 3rd party plugins. It would be good to set up an alternative mechanism for providing this support before this is deprecated. See #4779 for details.

---

PR Author Checklist (see the contributor guidelines for more details):

• my pull request is self-contained
• I've added tests for the changes I made
• I've applied code formatting (you can use mvn process-resources to format from the command line)
• I've squashed my commits where necessary
• every commit message starts with the issue number (GH-xxxx) followed by a meaningful description of the change

[hmottestad]

@edwardsph looks like you might need to sign the eclipse contributor agreement: https://github.com/eclipse-rdf4j/rdf4j/blob/main/CONTRIBUTING.md#eclipse-contributor-agreement

[hmottestad]

Could you add a comment explaining that these RDFa settings are in use by some users and referencing this issue: #4779

Please use a full link to the issue.

[hmottestad]

Could you add a comment explaining that these RDFa settings are in use by some users and referencing this issue: #4779

Please use a full link to the issue.

[hmottestad]

Don't worry about the dash license issue, it's just a problem with the tool.

[edwardsph]

Adding comments into code to link to the issue

[hmottestad]

Adding comments into code to link to the issue

Thanks @edwardsph :)

[hmottestad]

@edwardsph could you run mvn process-resources to format the code correctly and push a new commit?