Allow passing arbitrary event types to the rate limiter

[stayallive]

This allows us to re-use the rate limiter in: getsentry/sentry-php-agent#16

Since we already store arbitrary rate-limits anyway it makes sense we can also check for them instead of only the ones we have defined in our event type enum.

With PHP's type juggling this might not be a breaking change unless strict_types is defined. Unsure if we can make this change. Nevermind, we can remove any breaking concern by just doing what I've done in now 👍