This commit makes it possible to use the ${var} syntax to refer to
variables in the payload of the message in the collection field.
This makes it possible to select which collection to insert into
dynamically.
Fixes:
https://emqx.atlassian.net/browse/EMQX-9246
Fixes https://emqx.atlassian.net/browse/EMQX-9392
The returned information does not allow to diagnose the issue (i.e.: a
connection issue due to the wrong host and port, the wrong password
failing authn). However, such information is printed to the logs.
This changes the returned error to the API so that the user is hinted
at looking at the logs for further investigation of the error.