Add Feature flag for Anoncreds

[elribonazo]

Proposed feature

We want to enable feature flag for some of our features, the main reason is because we want to enforce developers to manually opt-in.

The reasons behind this is mainly to simplify our ecosystem by disabling some features by default. This does not mean they are not working but, probably there's some known issues or code quality improvements that should happen before we consider this as passed the experiment.

We may also want to have a generalized system to enable other feature flags across the SDK and have an easy way to validate this functionality.

Feature description

Feature flags will be a configuration parameter in the Agent Options and we will use booleans to disable or enable opt-in to the specific feature (anoncreds)

If Anoncreds is not manually opted-in by the Identus developer we will throw an exception if Anoncreds is used in any of our flows.

Ex) Disabled flag, Holder receives Anoncreds Credential, Offer or Presentation. Error is thrown because the feature is not active.

Anything else?

No response