Feature request: Please add enumerate secrets to each backend provider

Please add enumerate secrets to each backend provider.

My use case is a credentials manager. If I use only keyring, then I have to keep track of the list of credentials the user created outside of the backend provider, when best I can tell all the backend providers support enumerating the name of all the credentials.

Thanks, I've been using this project for all the places where I used to use .env files.

Start by surveying the backend provider implementations and the existing public keyring API to see how credential names are currently created and retrieved. Compare provider capabilities and define a consistent enumeration interface, including behavior when a provider cannot enumerate secrets. Done means the interface works across supported providers and has coverage for the resulting behavior.

Written by the indexing model from the issue text.