Generate Markdown + Asciidoc for Tasks and Pipelines

Feature request

Add ability for tkn to generate a Markdown representation of any Task, Pipeline, or group of such objects (ex: hub, bundle).

Use case

• Generate Markdown docs that can be rendered into HTML with a static site generator, such as hugo.
• Generate asciidoc docs that can be rendered to HTML by a supported platform.
• Auto-generate the READMEs for task/pipeline catalogs.

These would likely need to provide a default template that can be configured/modified by an end user. crd-ref-docs provides a similar mechanism.

UI Example

tkn bundle doc <bundle> [task/pipeline] [name] --output=markdown
tkn pipeline doc <name> -o markdown
tkn task doc <name> -o markdown

Note: there are some inconsistencies in command naming conventions for hub that make this a bit more challenging.

Review the existing tkn task, pipeline, and bundle command entry points, including the inconsistent hub command naming. Define the supported object groups, Markdown and Asciidoc output modes, and configurable default-template behavior; done means these commands can generate catalog-ready documentation for the requested objects.