cli: deprecate Errors type

The Errors type is no longer used by the CLI itself, and this custom
"multi-error" implementation had both limitations (empty list not being
`nil`), as well as formatting not being great. All of this making it not
something to recommend, and better handled with Go's stdlib.

As far as I could find, there's no external consumers of this, but let's
deprecate first, and remove in the next release.

Signed-off-by: Sebastiaan van Stijn <github@gone.nl>

Author: thaJeztah

cli/error.go

@@ -8,6 +8,8 @@ import (
 // Errors is a list of errors.
 // Useful in a loop if you don't want to return the error right away and you want to display after the loop,
 // all the errors that happened during the loop.
+//
+// Deprecated: use [errors.Join] instead; will be removed in the next release.
 type Errors []error
 
 func (errList Errors) Error() string {