Extend `docgen` tool to generate a JSON schema for `v1alpha1.Config` if a new optional cli arg is provided.
Extend the YAML-structured code comments on config fields to allow overriding the generated schema.
Add custom schemas for complex types.
Related to siderolabs/talos#6705.
Signed-off-by: Utku Ozdemir <utku.ozdemir@siderolabs.com>