build: split dev-infra configuration into individual files (#37890)

Splits the dev-infra configurations into individual files inside the
`.ng-dev/` folder. This helps with clarity as there is no single
configuration file that becomes extremely large and difficult to
maintain.

Additionally, more explicit configuration types are now used. This
fixed the max-line length setting for commit message validation.
This option is currently named incorrectly and a noop.

PR Close #37890

.ng-dev/github.ts

@@ -0,0 +1,11 @@
+import {GithubConfig} from '../dev-infra/utils/config';
+
+/**
+ * Github configuration for the `ng-dev` command. This repository is used as
+ * remote for the merge script and other utilities like `ng-dev pr rebase`.
+ */
+
+export const github: GithubConfig = {
+  owner: 'angular',
+  name: 'angular'
+};