chore: added more examples illustrating the use of Authorization Servers (AS) and Resource Servers (RS) in this specification

[peppelinux]

this PR is merely editorial and aims to resolve the issue #311

[jogu]

Discussed on today's WG call:

1. There was a consensus that splitting the credential issuer & the AS in the diagrams is a good idea
2. However we felt that the credential issuer should be to the right of the authorization server, as in most oauth sequence diagrams the resource server is shown on the right hand side of the authorization server and it was felt it would help people's mental models if we followed that convention.
3. If we're going to add AS to this diagram, then we should add it to all diagrams (I think there's only one other diagram)

[jogu]

as per my above comment

[peppelinux]

I can do that during the next week, thank you for the feedback

[peppelinux]

@jogu I did the requested changes here: 0521a83

[Sakurann]

thank you, Giuseppe!