Remove `AddProvider` method overloads with optional secret mutation function

[stijnmoreels]

Is your feature request related to a problem? Please describe.
When designing the secret store, we first had a single option to mutate the secret name. As this grew, we chose to use an options model to register ISecretProvider implementations, making these methods obsolete.

Describe the solution you'd like
Remove the AddProvider method with a single optional secret mutation function in the SecretStoreBuilder.