JwtConfigurer should be fluent

[jgrandja]

The JwtConfigurer currently reads like this:

http
  .oauth2()
    .resourceServer()
      .jwt()
        .jwkSetUri(jwkSetUri)
      .jwt()
        .decoder(decoder);

However, it needs to read like this:

http
  .oauth2()
    .resourceServer()
      .jwt()
        .jwkSetUri(jwkSetUri)
        .decoder(decoder);

[jzheaux]

@jgrandja If you don't mind, I'll assign this to myself once I am working on it. That way, the community can jump in if they get to it before me.

[dnl50]

Implemented the suggested improvements in #5644