[Feature Request] Add the capacity of describing Signing credentials in Credential descriptions

[jmprieur]

Is your feature request related to a problem? Please describe.
CredentialDescriptions describe FIC, certificates, and secrets. It would be useful to also describe signing credentials, at least based on certificate

Describe the solution you'd like

• Add a string property named Algorithm.
• Add a SigningCredential property
• Add a SymmetricSecurityKey property
• When the Algorithm is provided, and the rest of the properties describe a certificate, the credential is usable as a signing-credential.

Describe alternatives you've considered
Have a new class derived from CredentialDescription.

[jmprieur]

@RojaEnnam : we can't add the SigningCredentials and SymmetricSecurityKey in the options, as:

• they are not simple types (Won't do well with AoT)
• they would draw a dependency of IdentityModel whereras at some point in the future, IdentityModel could well depend on this Abstraction assembly.