[Enterprise] Consolidate extensions folders and keep them around (#98486)

* WIP: copy approach

* Fix package name

* Do not ignore .keep for frontend extensions

* Add keep file for frontend extensions

* Tweak makefile to generate enterprise swagger or not

* Remove duplicate imports

* Add build extensions

* Add CMD extensions

* Add keep to e2e extensions

* Add .keep

* Reduce file structure changes

* Ignore boring crypto

* Add e2e extensions keep file

* Remove enterprise file

* Update .gitignore

* Move things around

* Update git ignore

* Consolidate backend extensions folder

* Move enterprise deps

* Update comment

* Do not use build tags

* Ignore setting enterprise

* Revert changes in makefile

* Revert package changes

* Add back extensions main.go

* Update git ignore

* Ignore spanner tests

* Trick ignore files only by git

* Add .ignore file to CODEOWNERS for frontend-ops

* Fix issue with noisy duplicate targets

pkg/build/cmd/util/argcount_wrapper.go

@@ -0,0 +1,17 @@
+package util
+
+import "github.com/urfave/cli/v2"
+
+// ArgCountWrapper will cause the action to fail if there were more than `num` args provided.
+func MaxArgCountWrapper(max int, action cli.ActionFunc) cli.ActionFunc {
+	return func(ctx *cli.Context) error {
+		if ctx.NArg() > max {
+			if err := cli.ShowSubcommandHelp(ctx); err != nil {
+				return cli.Exit(err.Error(), 1)
+			}
+			return cli.Exit("", 1)
+		}
+
+		return action(ctx)
+	}
+}