Connection Manager documentation

[coot]

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Description

This PR subsumes #3464.

• network-spec: added PeerSharing to list of node-to-node protocols
• network-spec: mux documentation
• network-spec: integrate Neil Davis changes
• network-spec: build release version with nix

Checklist

Quality

• [ ] Commit sequence makes sense and have useful messages, see ref.
• [ ] New tests are added and existing tests are updated.
• [ ] Self-reviewed the PR.

Maintenance

• [x] Linked an issue or added the PR to the current sprint of ouroboros-network project.
• [x] Added labels.
• [ ] Updated changelog files.
• [x] The documentation has been properly updated, see ref.