Execute Behat tests only for a single content graph adapter at a time

[bwaidelich]

With the introduction of the Neos.ContentGraph.PostgreSQLAdapter the behat tests have been adjusted to run against both implementations.

This was done for performance reasons mainly. But it has some drawbacks:

• Tests are far more complex because they have to keep state of multiple adapters in memory and compare them individually
• Failure resolution is more difficult because one has to determine the failing implementation from the (sometimes misleading) error message
• Currently the way to skip tests for certain adapters is to use the @adapters tag in the feature files – this concept can't be used for future 3rd party implementations
• Tests for multiple adapters can't be executed in parallel

I would suggest to simplify the implementation again and allow to specify the adapter via behat.yml configuration.
To allow certain tests to be skipped during development, we could either use an allow (or deny) list of tests in the configuration or introduce feature specific annotations (like @features=contentSubgraph.findDescendantNodes, contentSubgraph.findChildNodes or similar).

Note: Previously our CI took ~1.25 hrs to execute behat tests (for PHP 8.1 and 8.2 each). With the sync mode (activated with #4110) they take less than 15 minutes. Besides we could probably execute them in parallel

[mhsdesign]

Current workaround for only executing maria is to add

        if ($excludePostgres = true) {
            $adapterKeys = array_filter($adapterKeys, fn ($key) => $key !== 'Postgres');
        }

to \Neos\ContentRepository\Core\Tests\Behavior\Features\Bootstrap\EventSourcedTrait::beforeEventSourcedScenarioDispatcher

[nezaniel]

Has been adjusted in #4455; Which adapter to use can now be set via configuration

[nezaniel]

has been merged and thus is resolved