Enhanced error messages

[jkayani]

Is your feature request related to a problem? Please describe.
AVP can be very opaque about errors it encounters, such as:

• Backend configuration is invalid (i.e, Cannot find secret even though it's in the same namespace and has access #301 )

• Path to a secret is wrong (ex: IBM Cloud SM with an invalid secret type or group id in path)

Describe the solution you'd like
Better error messages that point users to where issues might be with config/YAMLs/etc.

Describe alternatives you've considered
Better docs

Additional context
Add any other context or screenshots about the feature request here.

[jkayani]

Also could be good to have a --verbose flag so that users can debug where things are going wrong with replacing secrets. Extra messages could be printed to stderr that way it wouldn't interfere with normal Argo CD plugin operation (printing only valid YAMLs to stdout)