Need Definitions &/or a Terminology Section

[pamelatech]

We will need to define terms - for example right now we use a term called "B2B SaaS Developer" and "B2B SaaS Application" - it seems clear that terms will change but we do need a place where our shared understanding is captured.

[dhs-BI]

I updated the definitions and committed to main without a PR. A mistake I won't make again.

New version is here.

[aaronpk]

We now have a document for terminology with a good start to the definitions.

https://github.com/openid/ipsie/blob/main/ipsie-terminology.md