Make it clearer that Redocly CLI is API description format agnostic

Is your feature request related to a problem? Please describe.

We support linting of a few different structures now, and especially since introducing AsyncAPI support in #1127, we should take care to make sure that the tool doesn't refer specifically to OpenAPI when it's actually any API description format.

Describe the solution you'd like

• Change the output of the linting command to not refer to OpenAPI specifically, either to be generic or to pick up and state the file type that was valid
• Review the language of the command parameters and help output to make sure that it is only specific about OpenAPI where we do only have support for thar format
• Update the documentation for Redocly CLI (yes, all of it) to adjust the wording to be "API description" where it makes sense

Describe alternatives you've considered

Hope that nobody notices

Start by locating the Redocly CLI documentation and searching it for references that assume OpenAPI is the only supported format. Review each occurrence in context, changing wording to “API description” where appropriate while preserving format-specific guidance. The work is done when the documentation consistently reflects the supported formats and format-specific references remain accurate.