Add Figures to Resource Server Docs

[jzheaux]

Fixes gh-8182

[rwinch]

The diagrams look good.

I'd consider another ticket to take a look at the overall structure of the document. Looking at the TOC it is surprising to me that how Opaque Token Authentication Works is in Minimal Configuration for Introspection -> RuntimeExpectations. I'd think that Resource server would have some sort of introduction that lead to JWT and Opaque support top level sections.

[jzheaux]

@rwinch Yes, I mulled over this for some time, and I think there's value in bumping it out in the hierarchy - perhaps into its own section.

Wherever it goes, I believe it's important to lead with examples, meaning that I believe it should follow the minimal sample. Following "Runtime Expectations" felt the most natural since that section is still in the business of talking about the minimal sample.

The documentation as it stands in this PR begins with a small amount of architectural overview about Bearer Token as a whole only because there is no example that can be formulated at that point in the docs. But, once we get to JWT and opaque token, we can show an example, say "now what did we just see?", and proceed with architectural detail.

I see this as quite similar to what the early servlet docs do: Start with a minimal boot example in section 8, and then go into detail on how things work in section 9.

[jzheaux]

Merged via e62b8a7 to master