Prevent ALL external events being selected as a source for event based processes if any single group of external events have also been selected as a source. In this configuration, the event based process should not be creatable/updateable. The FE will likely block this too

ATs:

• No event based process will be saved in elasticsearch that uses both the 'all' external events as well as a selection of a group of external events
• When events don't have a `group`, these can be selected as a bucket too, as long as no 'all' source has been included
• Update REST-API documentation with error status code description