Verify the content type of flatpak manifests

[vsedmik]

Problem Statement

New content_type field has been added to the container manifests and container manifests list so that users can differentiate between flatpaks and other container images. We should check the field is set properly for the flatpak manifests.

Solution

This PR extends test_sync_consume_flatpak_repo_via_library with this assertion.
Apart from that it also leverages the function_flatpak_remote fixture.

Related Issues

https://issues.redhat.com/browse/SAT-21691

PRT test Cases example

trigger: test-robottelo
pytest: tests/foreman/cli/test_flatpak.py -k 'test_scan_flatpak_remote or test_flatpak_pulpcore_endpoint or test_sync_consume_flatpak_repo_via_library'
Katello:
  katello: 11300

[vsedmik]

trigger: test-robottelo
pytest: tests/foreman/cli/test_flatpak.py -k 'test_scan_flatpak_remote or test_flatpak_pulpcore_endpoint or test_sync_consume_flatpak_repo_via_library'
Katello:
  katello: 11300

[Satellite-QE]

PRT Result

Build Number: 10113
Build Status: SUCCESS
PRT Comment: pytest tests/foreman/cli/test_flatpak.py -k test_scan_flatpak_remote or test_flatpak_pulpcore_endpoint or test_sync_consume_flatpak_repo_via_library --external-logging
Test Result : ========== 4 passed, 1 deselected, 133 warnings in 1935.23s (0:32:15) ==========