fix(@angular/cli): fix the URL for doc search

In #16846, the URL for docs search was updated to point to the
corresponding vX.angular.io website (with an appropriate query for the
search). However, on the archive versions of the website (i.e. versions
older than the current stable), non-docs pages (including the home page)
are redirected to `/docs` (losing the query params).

This commit fixes the URL to include `/docs`, so that it is not
redirected (and preserve the query params that will trigger the search).

(cherry picked from commit 1beb582)

packages/angular/cli/commands/doc-impl.ts

@@ -47,7 +47,7 @@ export class DocCommand extends Command<DocCommandSchema> {
     let searchUrl = `https://${domain}/api?query=${options.keyword}`;
 
     if (options.search) {
-      searchUrl = `https://${domain}/?search=${options.keyword}`;
+      searchUrl = `https://${domain}/docs?search=${options.keyword}`;
     }
 
     // We should wrap `open` in a new Promise because `open` is already resolved