Accept header value shoud be case-insensitive

[antoinebesnardof]

Environment

• PostgreSQL version: 10.0.7
• PostgREST version: docker image postgrest/postgrest:v12.0.2
• Operating system: Linux

Description of issue

When specifying an Accept header with value Application/json (with an uppsercase letter at beginning) , PostgREST returns a 415 - Unsupported Media Type with content:

{
    "code": "PGRST107",
    "details": null,
    "hint": null,
    "message": "None of these media types are available: Application/json"
}

As stated in RFC 7231, Media Types are case-insensitive.

PostgREST may then use the application/json Media Type Handler.

Thank you for all this work.