[Why]
In order to make `khepri_db` the default in the future, the handling of
`$RABBITMQ_FEATURE_FLAGS` had to be adapted to be able to *disable*
Khepri instead.
Unfortunately I broke the behavior with stable feature flags that are
only available in the primary umbrella. In this case, they were
automatically enabled and thus, clustering with an old umbrella that did
not have these feature flags failed with `incompatible_feature_flags`.
[How]
The solution is to always use an absolute list of feature flags, not the
new relative list.
V2: Allow a testsuite to skip the configuration of the metadata store.
This is needed for the feature_flags_SUITE testsuite because it
tests the default behavior and the configuration of the metadata
store changes that behavior.
While here, fix a ct log message where variables were swapped
compared to the format strieg expectation.
V3: Enable `rabbitmq_4.0.0` feature flag in rabbit_mgmt_http_SUITE. This
testsuite apparently requires it and if it's not enabled, it fails.
57ed962ef6