Extend GitHub actions

[gabinoumbe]

[gabinoumbe]

This issue is handled with the following key improvements:

1. GitHub actions workflow for plugin integration

• build and test jobs have been created on matrix strategy for different JDK versions and mapping service versions.
• a generated .jar file is built and reused between jobs.
• a dockerized integration testing ensures the plugin runs inside the mapping service container.

2. Dynamic JSON Payloads

• two temporary JSON files, record.json and document.json, are generated as part of the test job.
• these files are passed via [MultipartFormData] to Hurl for the plugin (mapping scheme) creation
• the cleanup step allow to delete the temporary files after the testing phase.

3. basic.hurl updates

• removing the manual --boundary definitions and replace by the [MultipartFormData] syntax.