Move CGO requirement to the effected code

Forcing `CGO_ENABLED=1` in the Makefile is too far away from the reason
we do it. Use a build constraint instead with a comment and link.

See: 67fe735

Makefile

@@ -145,7 +145,7 @@ deploy-dev: createnamespaces
 ##@ Build - Binary
 .PHONY: build-postgres-operator
 build-postgres-operator: ## Build the postgres-operator binary
-	CGO_ENABLED=1 $(GO_BUILD) $(\
+	$(GO_BUILD) $(\
 		) --ldflags '-X "main.versionString=$(PGO_VERSION)"' $(\
 		) --trimpath -o bin/postgres-operator ./cmd/postgres-operator
 

internal/postgres/users.go

@@ -2,6 +2,9 @@
 //
 // SPDX-License-Identifier: Apache-2.0
 
+// [pg_query.Parse] requires CGO to compile and call https://github.com/pganalyze/libpg_query
+//go:build cgo
+
 package postgres
 
 import (