docs: docusaurus/credentials refactor

[mixmix]

I'm preparing some docs for "connectionless" credentials. In trying to make space for them I noticed that this area in the docs was gonna get messy.

My solution (in preparation) was to refactor the docs (and assets) around credentials with 2 new patterns:

1. group credential path type

• didcomm
• oid4vc
• connectionless (new, coming soon)

2. change asset naming to be explicit, and group

For format for file-names in these folders like <flow>.<implementation>.<file-extension>

new	old
issue-flow.jwt.png	issue-flow.png
issue-flow.anoncreds.png	anoncreds-issue-flow.png

Here's what the workup looks like

├── credentials
│   ├── connectionless                          // << COMING SOON (placeholder)
│   │   ├── issue.md
│   │   └── present-proof.md
│   ├── didcomm
│   │   ├── anoncreds-setup.png                 // << unused?
│   │   ├── anoncreds-setup.puml
│   │   ├── issue-flow.anoncreds.png
│   │   ├── issue-flow.anoncreds.puml
│   │   ├── issue-flow.jwt.png
│   │   ├── issue-flow.jwt.puml
│   │   ├── issue.md
│   │   ├── present-proof-flow.anoncreds.png
│   │   ├── present-proof-flow.anoncreds.puml
│   │   ├── present-proof-flow.jwt.png
│   │   ├── present-proof-flow.jwt.puml
│   │   └── present-proof.md
│   ├── oid4cv
│   │   └── issue.md
│   └── revocation.md

[mixmix]

Question: not sure where anoncreds-setup.* should live...