Support limiting ReservedConcurrentExecutions for Lambda invocations

[dominikschubert]

Still not fully prod ready.

There are some drawbacks to using this approach but I think it's the least intrusive in regards of changes to the old Lambda provider since it reuses the locks "register" that was introduced previously for handling event source mapping concurrency.

Not very happy with the test pattern here yet, since it leads to a fairly long test execution duration of about a minute. It does cover a few different scenarios though and I'd love to introduce a better "parallel invocation" counter soon to validate how async (Event type) invokes are processed by the Lambda service.