Improve Hub plugin definition contribution docs

Background

https://docs.meltano.com/contribute/plugins should explain exactly how to build a plugin definition for the Hub, including new values like requires (https://github.com/meltano/meltano/issues/6106), and the new usage/prereq/settings_preamble properties that build the detail pages.

Spec

To add to plugin definition reference (the yaml stuff):

• requires
• settings - and how this relates to config
• capabilities - and how tap developers can determine the correct capabilities
• container_spec - per https://github.com/meltano/meltano/issues/6408#issuecomment-1190924489

Hub-only YAML fields:

• prereqs markdown field
• settings_preamble markdown field
• usage markdown field

To add to contributing docs:

• Link to plugin reference page.
• Instructions for submitting.
• Details on how the markdown will be rendered in our readmes docs.
• A small blurb on how we capture metrics for the hub.
• Details on how this shows up on the REST API.
• Info on how users will install the plugin after it is published.

[aaronsteers]

That makes sense. I do think the hub should have a page pointing to the Meltano one then.

[edgarrmondragon]

I’m imagining a yaml reference for plugins modeled after this GitHub Yaml Workflow Reference.

@aaronsteers what’s they say about great minds? That’s what I went for in https://github.com/meltano/meltano/pull/6460 😅

For what it’s worth, I did also investigated automated approached to document the yaml reference based on our JSON Schema, but none of these investigations came up with fruitful/usable libraries.

I did think about that but came similarly with no out-of-the-box solutions.