*: Bump module version to v2

[timflannagan]

Description

Bump the go.mod module version to /v2 now that we agreed on a v2.x tagging convention. Unfortunately, Go is very strict about this scenario (despite an entirely new module name) when I tested this out locally:

$ mkdir kgateway-import-test && cd kgateway-import-test
$ cat > main.go << 'EOF'
package main

import (
    "fmt"
    _ "github.com/kgateway-dev/kgateway"
)

func main() {
    fmt.Println("Testing kgateway import")
}
EOF

$ go mod init example.com/kgateway-import-test
go: creating new go.mod: module example.com/kgateway-import-test
go: to add module requirements and sums:
	go mod tidy

$ # Attempt to get the module directly (this fails)
$ go get github.com/kgateway-dev/kgateway@v2.0.0-main
go: github.com/kgateway-dev/kgateway@v2.0.0-main: invalid version: module contains a go.mod file, so module path must match major version ("github.com/kgateway-dev/kgateway/v2")

# Attempt to tidy the module (this also fails)
$ go mod tidy
go: finding module for package github.com/kgateway-dev/kgateway
go: toolchain upgrade needed to resolve github.com/kgateway-dev/kgateway
go: github.com/kgateway-dev/kgateway@v1.17.16 requires go >= 1.22.7; switching to go1.22.12
go: finding module for package github.com/kgateway-dev/kgateway
go: found github.com/kgateway-dev/kgateway in github.com/kgateway-dev/kgateway v1.17.16
go: example.com/kgateway-import-test imports
	github.com/kgateway-dev/kgateway: github.com/kgateway-dev/kgateway@v1.17.16: parsing go.mod:
	module declares its path as: github.com/solo-io/gloo
	        but was required as: github.com/kgateway-dev/kgateway

Testing this using the following script:

cat scratch/update-imports.sh           
#!/bin/bash

set -e

# Find all .go files and update the import paths
find . -type f -name "*.go" -exec sed -i.bak 's|"github.com/kgateway-dev/kgateway/|"github.com/kgateway-dev/kgateway/v2/|g' {} \;
find . -name "*.bak" -type f -delete

# Update go.mod (already done, but just to be safe)
sed -i.bak 's|module github.com/kgateway-dev/kgateway$|module github.com/kgateway-dev/kgateway/v2|g' go.mod
rm -f go.mod.bak

# Run go mod tidy to clean up dependencies
go mod tidy%                                                                                                                                                

Checklist:

• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• I have added tests that prove my fix is effective or that my feature works

[timflannagan]

Related to #10607. I'll close that issue out once I re-test locally.