Add mechanism for user to disable HTTP/2 if required

[ciarams87]

As a user of NGF
I want a way to disable HTTP/2 support in my NGF deployment
So that I can remove this support if security vulnerabilities are found in HTTP/2 functionality in NGINX

A/C:

• A config option is provided so that HTTP/2 support can be disabled if required
• If HTTP/2 is disabled and a GRPCRoute is deployed, the GRPCRoute's status is reported at Not Accepted.

Dev Notes:

• This should likely be part of the NginxProxy CRD