CI/CD rust documentation generation

[agouin]

Is your feature request related to a problem? Please describe. CI/CD pipeline that will produce rendered output for the following documentation:

• Protocol specification (mdbook) to protocol.penumbra.zone
• User documentation (mdbook) to guide.penumbra.zone
• Rust API docs (cargo doc) to rustdoc.penumbra.zone
• Protobuf docs to protobuf.penumbra.zone

Describe the solution you'd like Add github actions that will create artifacts (either direct artifacts or a URL to the rendered content) for the documentation.

Describe alternatives you've considered Checkout the specific branch locally and build the rendered documentation.

Additional context N/A