request: add support for parsing and matching suffixes

Since the times of XML media often have a suffix, for example `application/vnd.oai.openapi+json`. This conveys separate information on syntax and semantics.

Ability to match by group and suffix (in the example: `application`, `json`) would let applications to communicate the exact media type, and libraries to process such content in a generic way.

The issue names no files, tests, or entry points. Start by locating the Python media-type parsing and matching functions and their tests, then trace how `application/vnd.oai.openapi+json` is handled; done means matching can use its group and `json` suffix while preserving the complete media type.

Scritto dal modello di indicizzazione a partire dal testo della issue.