remove old gloo code

[lgadban]

As we continue bootstrapping the initial kgw standalone builds, we need to:

1. properly define the go module
2. remove legacy gloo edge/non k8s gateway api related code

In order to properly do 1, we will have to fix ALL internal imports.
Since we also need to take care of 2, it makes little sense to spend the time fixing the broken imports for dead code that is ultimately destined for the bit bucket.

We can accomplish this wholesale by:

1. deleting the majority of the code not contained in the projects/gateway2 directory
2. renaming the go mod
3. fixing the leftover code imports

[lgadban]

Follow ups:

• Envoy Filter code
• envoy API protos
• envoy-gloo API protos
  • just importing from main now, but how does the release branch work?

global settings:

• regex stuff / program size

[lgadban]

track major functionality being removed:

• helm unit tests

[lgadban]

removing in-memory tests that live in test/e2e as they will need to rewritten entirely anyway to use the new framework
see: #10480 (comment)

[lgadban]

more PRs to come, reopening