Rework OpenPayments documentation

[huijing]

We are in the process of migrating our OpenPayments documentation from readme.io over to our own hosted Starlight documentation site. This will happen as the actual content of the documentation is being updated.

Related issues to track:

• Synced tabs withastro/starlight#462 Synced tabs withastro/starlight#953
• Component overrides feedback withastro/starlight#861 Improve custom page injection withastro/starlight#982
• Copy button for Code Blocks withastro/starlight#461
• Certain fields are not parsed correctly HiDeoo/starlight-openapi#12

Feature requirements

1. Parse OpenAPI specification YAML into documentation pages (using https://github.com/HiDeoo/starlight-openapi)
2. Be able to pull code snippets directly from https://github.com/interledger/open-payments-snippets, code should be able to be chunked up for easier explanation (built components for these)
3. Ability to sync tabs such that code snippets of the selected language all are active at the same time (see Synced tabs withastro/starlight#953)

Blocking issues

1. The plugin we are using does not parse all the fields in our specification as expected (see Certain fields are not parsed correctly HiDeoo/starlight-openapi#12) (Fixed)
2. The most updated version of the plugin has an issue where the sidebar is unable to render (see Improve custom page injection withastro/starlight#982) (not exactly blocking per se)