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