Refactor testsuite to be more aligned with Gateway API

[pehala]

• New structure contains these fixture/parts
  • backend() + Httpbin class - Backend to which the requests should get routed
  • gateway() fixture + Gateway class - Equivalent of Gateway object in Gateway API
  • route() fixture + GatewayRoute class - Equivalent of HTTPRoute object in Gateway API
  • exposer() fixture + Exposer class - Responsible for exposing hostname to be accessible outside of a cluster
    • For Service Protection only, it is be OpenShiftExposer, which uses OpenShift routes
    • For MGC it is DNSPolicyExposer, which relies on DNSPolicy to do the heavy lifting and expose the actual hostname
  • hostname() fixture and Hostname class - Exposed Hostname, for which we can create HTTP client to send requests
• Redone pure Envoy deployment
  • Make to emulate how Gateway API works - it is now slower due to a few rollouts needed
  • Update config instead of having to create new template file for each configuration (e.g. Wristband and TLS)
• Simplified some tests due to the new structure

[jsmolar]

move objects.__init__ to openshift.

[averevki]

LGTM