Merge api/ref/types and api/ref/metadata pages and correct links, including from generated context docs

[kriswest]

The division of the utility types used as arguments or return values from API calls into types and metadata is somewhat arbitrary, are not reflected in the sourcecode they represent and can be confusing. Further, it makes it very hard to generate links to the right documentation pages from other generated documentation (Context type references pages are now generated from the schema files).

I propose that we:

• Merge the types and metadata pages together and stick to 'types'
• Configure a docusuaurus redirect for 'metadata' page links to the 'types' page
• Update the generated pages for context docs to create links for any API types (e.g. on the Action page):

[kriswest]

I think this is probably how you set-up redirects in docusaurus: https://docusaurus.io/docs/api/plugins/@docusaurus/plugin-client-redirects