Wrap errors in validation check for server/config.go

Currently determining which service is causing a validation error https://github.com/influxdata/kapacitor/blob/master/server/config.go#L240-L362 isn't possible.

Errors should be wrapped for additional context.

Start by reading the validation code in server/config.go around lines 240-362 and trace how errors are returned for each service. The work is done when validation errors identify the service that caused them through additional context; check the repository's existing validation coverage if available.

Written by the indexing model from the issue text.