Create the REST API compatibility tests pipeline

As described by TL-310, implement the REST API Compatibility Tests Pipeline:

• Pull the Nuxeo image and start the server.
• Run the tests from the rest-api-compatibility-tests GitHub repository.

As done for Nuxeo JSF UI, triggers the REST API Compatibility Tests Pipeline from a nuxeo/nuxeo PR to validate that the PR does not break anything.

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We now have a multibranch pipeline with the following behavior:

• Triggered by a PR on nuxeo/rest-api-compatibility-tests: run tests against nuxeo/nuxeo:11.x and set status check on the PR.
• Triggered by the master branch of nuxeo/rest-api-compatibility-tests: run tests against nuxeo/nuxeo:11.x, set status check on master and notifies #platform-notifs in case of failure or success after failure.
• Triggered by a PR on nuxeo/nuxeo, in a stage following the Docker build and test: run tests against nuxeo/nuxeo:PR-4555-11.5-SNAPSHOT (for instance) and set status check on the nuxeo/nuxeo PR (required).
• Triggered by the master branch of nuxeo/nuxeo: run tests against nuxeo/nuxeo:11.x, set status check on the master branch of nuxeo/nuxeo and notifies #platform-notifs in case of failure or success after failure.