refactor(dev-infra): move existing env-stamp command into subfolder (#38656)

Moves the existing `ng-dev release env-stamp` command into a
subfolder so that the staging/publish tool can have its own
dedicated folder (without being polluted by the env-stamp logic).

Every subcommand should be in its own folder.

PR Close #38656

dev-infra/release/cli.ts

@@ -6,12 +6,17 @@
  * found in the LICENSE file at https://angular.io/license
  */
 import * as yargs from 'yargs';
-import {buildEnvStamp} from './env-stamp';
+
+import {buildEnvStamp} from './stamping/env-stamp';
 
 /** Build the parser for the release commands. */
 export function buildReleaseParser(localYargs: yargs.Argv) {
-  return localYargs.help().strict().demandCommand().command(
-      'build-env-stamp', 'Build the environment stamping information', {}, () => buildEnvStamp());
+  return localYargs.help()
+      .strict()
+      .demandCommand()
+      .command(
+          'build-env-stamp', 'Build the environment stamping information', {},
+          () => buildEnvStamp());
 }
 
 if (require.main === module) {