Java17 and modernize

[axl8713]

These changes stem from the work made from georchestra in #82.

Migrate to Jakarta EE / Apache HttpClient 5 / Java 17, add Docker support

• Migrate servlet API from javax.* to jakarta.* (Jakarta EE 10)
• Upgrade Apache HttpClient 4 → 5; update all execute(request) calls to the response-handler overload
• Target Java 17 (downgraded from Java 21); update CI accordingly
• Bump all dependencies (commons-fileupload2, Jetty EE10, etc.)
• Add Dockerfile and Main.java standalone entry point (from georchestra PR)
• Code cleanup
• Test code modernization

When this get merged, these changes will overseed the ones in #82, that then could be closed.