Support for external custom authention extension

[Thisara-Welmilla]

Is your feature request related to a problem? Please describe.

Considering IS, Asgardeo, and PIC, it's a common requirement to have a capability to authenticate users with a custom authenticator that we do not provide out of the box. Currently:
For IS, the IAM developer must create an authenticator extension and add it as a binary to the product and for Asgardeo, there is no way to accomplish this.

Describe the solution you would prefer

This feature is intended to provide support for user authentication via an external custom authentication service. Such authenticator can be added to application login flow.
The product should define a contract defined for this flow that the service that extends need to implement.

Implementation Tasks:

• Support configuring the external authenticator properties with action feature Improve Action feature to utilized by the authentication extension #20931
• Bring in prepost and inflow action separation action management so that custom authenticator can be considered as inflow action Categorize action types as prepost and inflow #21384
• Custom authenticator adapter for user authentication with external service Custom authenticator adapter for user authentication with external service  #20887
• Introduce new authenticator properties: DefinedBy to indicate whether authenticator is SYSTEM or User Defined Introduce new authenticator properties: DefinedBy #21111
• Provide support for the new cutsom authentication management Provide API for the new custom authentication management #21216
• Improve UI to incorporate authentication flow with the external authentication service Improve UI to incorporate authentication flow with the external authentication service #20893
• Implement and e2e test for the new authenticator usages
• Documentation on external authentication service [DOC] Provide support for external custom authention extension. #21036