refactor(dev-infra): move common versioning tooling to shared location (#38656)

We initially added logic for determining active release trains into
the merge script. Given we now build more tools that rely on this
information, we move the logic into a more general "versioning" folder
that can contain common logic following the versioning document for the
Angular organization.

PR Close #38656

.ng-dev/merge.ts

@@ -1,6 +1,7 @@
 import {DevInfraMergeConfig} from '../dev-infra/pr/merge/config';
 import {getDefaultTargetLabelConfiguration} from '../dev-infra/pr/merge/defaults';
 import {github} from './github';
+import {release} from './release';
 
 /**
  * Configuration for the merge tool in `ng-dev`. This sets up the labels which
@@ -13,7 +14,9 @@ export const merge: DevInfraMergeConfig['merge'] = async api => {
     mergeReadyLabel: /^action: merge(-assistance)?/,
     caretakerNoteLabel: 'action: merge-assistance',
     commitMessageFixupLabel: 'commit message fixup',
-    labels: await getDefaultTargetLabelConfiguration(api, github, '@angular/core'),
+    // We can pick any of the NPM packages as we are in a monorepo where all packages are
+    // published together with the same version and branching.
+    labels: await getDefaultTargetLabelConfiguration(api, github, release),
     requiredBaseCommits: {
       // PRs that target either `master` or the patch branch, need to be rebased
       // on top of the latest commit message validation fix.