shellcheck: add config

[euclio]

No description provided.

[euclio]

Fixed, though I wonder if this could be done automatically in the future (i.e., the configured messages are prepended with [${sourceName}]. That way it could be made configurable, too.

[creativenull]

This would depend on diagnosticls itself, I'll see what I can do on my side. So far I've pretty much observed that by default the message does not include the linter name so I started to include the name manually on the config side.