docs(codegen): document the config option types in `src/types.ts`

[aryaemami59]

Part of #5368.

Document the config option types in src/types.ts - Config, CommonOptions,
OutputFileOptions, EndpointOverrides, the matcher types, and the exported
string-union types.

This is the source of truth the docs page is generated from by hand, so it is the
highest-leverage file to document first.

Blocked on the tagging-convention question in
#5368: whether to apply
@public +
@since to exported symbols and
@internal to non-exported ones. If that is
declined, this becomes a plain descriptive JSDoc pass with no tags.

Fixed by #5373.