Enable custom SecretManagers

[DeppLearning]

Description

This issue still persists: #407 . The closing PR #462 mentioned the issue of using custom secret managers wasn't resolved yet, still the issue was closed.

Motivation

The available variants in the SecretManager enum are not enough, and it would help adoption if there would be a generic api that others can implement without needing to fork.

Requirements

• We would want to be able to pass custom secret managers. We don't mind if that is achieved by dropping the enum entirely in favor of using just the traits, or extending the enum (this used to work, but I think it doesn't anymore: DeppLearning@f174a90#diff-4837978b4d3d1c2f1b96b18e96e29ec5a50a32867735eb9bee9981528b888d5fR121)

Open questions (optional)

Are you planning to do it yourself in a pull request?

Maybe

[thibault-martinez]

Hi @DeppLearning, it was closed because it will not be addressed on 1.0 and is already being implemented on 2.0.

[DeppLearning]

Hi @DeppLearning, it was closed because it will not be addressed on 1.0 and is already being implemented on 2.0.

Oh I missed that, thank you for the clarification