refactor(dev-infra): use a mixin to require a github-token for an ng-dev command (#38630)

Creates a mixin for requiring a github token to be provided to a command.  This mixin
allows for a centralized management of the requirement and handling of the github-token.

PR Close #38630

dev-infra/utils/yargs.ts

@@ -0,0 +1,37 @@
+/**
+ * @license
+ * Copyright Google LLC All Rights Reserved.
+ *
+ * Use of this source code is governed by an MIT-style license that can be
+ * found in the LICENSE file at https://angular.io/license
+ */
+
+import {Argv} from 'yargs';
+import {error, red, yellow} from './console';
+
+export type ArgvWithGithubToken = Argv<{githubToken: string}>;
+
+export function addGithubTokenFlag(yargs: Argv): ArgvWithGithubToken {
+  return yargs
+      // 'github-token' is casted to 'githubToken' to properly set up typings to reflect the key in
+      // the Argv object being camelCase rather than kebob case due to the `camel-case-expansion`
+      // config: https://github.com/yargs/yargs-parser#camel-case-expansion
+      .option('github-token' as 'githubToken', {
+        type: 'string',
+        description: 'Github token. If not set, token is retrieved from the environment variables.',
+        coerce: (token: string) => {
+          const githubToken = token || process.env.GITHUB_TOKEN || process.env.TOKEN;
+          if (!githubToken) {
+            error(red('No Github token set. Please set the `GITHUB_TOKEN` environment variable.'));
+            error(red('Alternatively, pass the `--github-token` command line flag.'));
+            error(yellow(`You can generate a token here: ${GITHUB_TOKEN_GENERATE_URL}`));
+            process.exit(1);
+          }
+          return githubToken;
+        },
+      })
+      .default('github-token' as 'githubToken', '', '<LOCAL TOKEN>');
+}
+
+/** URL to the Github page where personal access tokens can be generated. */
+export const GITHUB_TOKEN_GENERATE_URL = 'https://github.com/settings/tokens/new';