Feat: Slow query configuration

[fullstackfool]

The slow query logging uses 500ms when manually activating via ray()->slowQueries();. When activated via the ray.php config SEND_SLOW_QUERIES_TO_RAY value, however, it defaults to 0ms causing all queries to be logged.

This adds a configurable RAY_SLOW_QUERY_THRESHOLD=500 to the ray.php stub.

Additionally, the composer.json offered format script, but cs-fixer was not included in the dev dependencies.

[fullstackfool]

Regarding tests, there are currently no tests that confirm the propagation of ray.php stub values, so unsure as to the requirement here.

[fullstackfool]

Accompanying docs update: spatie/ray#718

[freekmurze]

Thanks!

[fullstackfool]

Thank you for the adjustments & merge @freekmurze 🎉