Process Applications Sync Between Desktop and Web Modeler

[philippfromme]

Problem you would like to solve

Users should be able to sync process applications between desktop and web modeler.

• when downloading a process application from web modeler it should be recognized as a process application by the desktop modeler
• when uploading a process application created with desktop modeler it should be recognized as a process application by the web modeler

Proposed solution

• agree on what a process application is (e.g. a .camunda-process-application file in a directory)
• include this file when downloading a process application from web modeler
• actualy sync not to be done through desktop modeler but e.g., Git

Alternatives considered

None.

Additional context

Related to #2508