selftest/bblayers: Add a test to validate bitbake-setup registry schema

selftest/bblayers: Add a test to validate bitbake-setup registry schema

This test validates bitbake/default-registry/configurations/*.conf.json
against bitbake-setup.schema.json:
INFO - test_validate_bitbake_setup_default_registry (bblayers.BitbakeLayers.test_validate_bitbake_setup_default_registry)
DEBUG - Validating .../poky/bitbake/bin/../default-registry/configurations/oe-nodistro.conf.json
DEBUG - Validating .../poky/bitbake/bin/../default-registry/configurations/poky-master.conf.json
INFO -  ... ok
INFO - test_validate_examplelayersjson (bblayers.BitbakeLayers.test_validate_examplelayersjson)
INFO -  ... ok
INFO - ----------------------------------------------------------------------
INFO - Ran 2 tests in 110.469s
INFO - OK
INFO - RESULTS:
INFO - RESULTS - bblayers.BitbakeLayers.test_validate_bitbake_setup_default_registry: PASSED (0.92s)
INFO - RESULTS - bblayers.BitbakeLayers.test_validate_examplelayersjson: PASSED (0.19s)
INFO - SUMMARY:
INFO - oe-selftest () - Ran 2 tests in 110.469s
INFO - oe-selftest - OK - All required tests passed (successes=2, skipped=0, failures=0, errors=0)

Signed-off-by: Yoann Congal <yoann.congal@smile.fr>
Signed-off-by: Mathieu Dubois-Briand <mathieu.dubois-briand@bootlin.com>