Remove the `SecretStoreSource` constructor with optional mutated secret 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 secret names before secret retrieval. As this grew, we chose to use an options model internally and expose the different options via method overloads, making this constructor obsolete.

Describe the solution you'd like
Remove the SecretStoreSource constructor with a single optional mutated secret function as parameter.