Add example/demo for multiple or dynamic origins

[abergs]

A number of issues and pr's has been asked over the years to support either multiple origins, subdomains or dynamic origin validation configured at runtime.

All these can be supported by initiating a new instance of the library with the proper configuration. This can be done either with a new Fido2(new config...)) or through DI with the use of a factory.

We currently don't have too many easy to copy/paste examples of this, so perhaps we should add one.

Related:

• Support dynamic "origins" for this library for testing #538 (reply in thread)
• Wildcard orgin url feature #583