Specific exception for retrieving missing required values from ConnectionFactoryOptions

[mp911de]

We should consider introducing a dedicated exception when retrieving a value from ConnectionFactoryOptions that is not present. Right now, IllegalStateException gets thrown. Although the state can be considered illegal, the exception should rather express a motivation and indication that they can do something about (e.g. adding the missing option).

We could introduce MissingOptionException that is either a subclass of R2dbcException or IllegalStateException and that holds also the requested Option in addition to its message.

From working with ConnectionFactoryOptions via ConnectionFactoryProvider, that exception (and associated error handling behavior) showed that the current IllegalStateException gets propagated into the user-space and users or applications get in touch with that exception.