OpenAPI 2.0: add linting rule for media type

[char0n]

Media Type is defined as https://github.com/OAI/OpenAPI-Specification/blob/main/versions/2.0.md#mime-types

Now the goal of this issue is to validate all media types as valid.

Part 1

Provide media type parser based on https://datatracker.ietf.org/doc/html/rfc6838 and it's ABNF grammar in similar manner as https://github.com/char0n/openapi-path-templating

Part 2

Utilize the parser to validate all media type within the definition.

---

Important

This might be also applicable to OpenAPI 3.0.x and OpenAPI 3.1.0. We need to verify as part of this issue.