src/app/shared/search: use nofollow for facet links

Use `rel="nofollow"` on Discovery search facet links to signal to
well-behaved bots that they should not crawl facets. Faceted search
results are derivative content of primary DSpace objects and cause
excessive load on the server and even exhaust your crawl budget on
crawlers like Google.

See: https://developers.google.com/search/blog/2024/12/crawling-december-faceted-nav
See: https://developers.google.com/search/docs/crawling-indexing/crawling-managing-faceted-navigation
(cherry picked from commit f1e4bf5)

Author: alanorth

src/app/shared/search/search-filters/search-filter/search-facet-filter-options/search-facet-option/search-facet-option.component.html

@@ -3,7 +3,8 @@
     [tabIndex]="-1"
     [routerLink]="[searchLink]"
     [queryParams]="addQueryParams$ | async"
-    (click)="announceFilter(); filterService.minimizeAll()">
+    (click)="announceFilter(); filterService.minimizeAll()"
+    rel="nofollow">
     <label class="mb-0 d-flex w-100">
       <input type="checkbox" [checked]="false" class="my-1 align-self-stretch filter-checkbox" role="checkbox" tabindex="0"/>
       <span class="w-100 ps-1 break-facet">