read/write secret option should reflect a list of all available secrets

[thesephirot]

the writesecret option shows an error if no "value" is provided

orbctl writesecret --gitops
Error: Key must be provided eighter by value or by file path or by standard input
Usage:
  orbctl writesecret [path] [flags]

it would be more convenient to show a list of the available fields (and which have been set already)

something like "list secrets" would also be intuitive.