cmd/containerboot: handle v6 pod ips that are missing square brackets (#18519)

This commit fixes an issue within containerboot that arose from the
kubernetes operator. When users enable metrics on custom resources that
are running on dual stack or ipv6 only clusters, they end up with an error
as we pass the hostport combintation using $(POD_IP):PORT.

In go, `netip.ParseAddrPort` expects square brackets `[]` to wrap the host
portion of an ipv6 address and would naturally, crash.

When loading the containerboot configuration from the environment we now
check if the `TS_LOCAL_ADDR_PORT` value contains the pod's v6 ip address.
If it does & does not already contain brackets, we add the brackets in.

Closes: #15762
Closes: #15467

Signed-off-by: David Bond <davidsbond93@gmail.com>

cmd/containerboot/settings_test.go

@@ -6,6 +6,7 @@
 package main
 
 import (
+	"net/netip"
 	"strings"
 	"testing"
 )
@@ -226,3 +227,30 @@ func TestValidateAuthMethods(t *testing.T) {
 		})
 	}
 }
+
+func TestHandlesKubeIPV6(t *testing.T) {
+	t.Setenv("TS_LOCAL_ADDR_PORT", "fd7a:115c:a1e0::6c34:352:9002")
+	t.Setenv("POD_IPS", "fd7a:115c:a1e0::6c34:352")
+
+	cfg, err := configFromEnv()
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	if cfg.LocalAddrPort != "[fd7a:115c:a1e0::6c34:352]:9002" {
+		t.Errorf("LocalAddrPort is not set correctly")
+	}
+
+	parsed, err := netip.ParseAddrPort(cfg.LocalAddrPort)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	if !parsed.Addr().Is6() {
+		t.Errorf("expected v6 address but got %s", parsed)
+	}
+
+	if parsed.Port() != 9002 {
+		t.Errorf("expected port 9002 but got %d", parsed.Port())
+	}
+}