S3Mock returns wrong error for invalid bucket names

[afranken]

In 2.4.16, S3Mock started enforcing valid bucket names.

400 - InvalidBucketName is returned as expected when creating a new bucket, but the other handler methods are using a simplified regular expression to match bucket names, and Spring will reply with a generic
"Error making request with Error Code MethodNotAllowed and Http Status Code MethodNotAllowed" because no suitable handler method can be found.

This alone is a problem already, but for example, if a test would request some key from some bucket without creating the bucket first, if the bucket name is invalid, S3Mock does not even check if the bucket exists, so the client never receives a valid error message.

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We could either:
Remove the regex from the path patterns of all handler methods
or:
Add a fallback handler method for all HTTP methods that do not apply the regex pattern and therefore check the bucket name and return a correct error message.

[afranken]

example issues: #928, #874