* docs: add guide to hide custom openapi extensions
* docs: update naming consistency in guide on how to hide openapi extensions
* Rename hide-custom-extensions.md to hide-specification-extensions.md
* docs: change custom extensions to specification extensions
- change file name and links
- change code
- change inline text links
- minor other changes
- fix OpenAPI capitalization
Co-authored-by: Adam Altman <adam@redoc.ly>
