[demo] Autogenerate documentation on JSON sent to templates/jq from weaver_forge

[jsuereth]

This creates a new utility, only intended to be used by weaver contributors, for generating documentation directly from SerDe / schemars configuration. These libraries leverage macros to read our own comments and produce a traversable schema.

UNFORTUNATELY, the schema is optimised for generating JSON schema, so it's actually poor for generating docs. This is ~2 hour attempt at doing something decent enough to evaluate if we want to invest in it. Alternatively, we could use schemars to generate docs and then fire these at an NPM utility that creates markdown from json schema.

Either way the goal of this PR is to:

• Provide human readable documentation over what JSON fields and types to expect in JQ and JINJA. Note: We can expand to Rego in the future.
• Provide an easy to run tool that will automatically update these docs when changes are made (via cargo run -p docgen)
• Discuss what we want human readable documentation to look like and minimum requirements

Towards: #692 and #693

[github-advanced-security]

clippy found more than 20 potential problems in the proposed changes. Check the Files changed tab for more details.