Add search publication page and fix category access

frontend/src/app/pages/search-publications/search-publications.component.html

@@ -0,0 +1,13 @@
+<h1>Search results</h1>
+@if((isLoading$ | async) === true) {
+    <h2>Search in progress...</h2>
+    <mat-spinner></mat-spinner>
+} @else if((isLoaded$ | async) === true) {
+    @if((publications$ | async)?.length) {
+        <app-publication-list [publications$]="publications$"></app-publication-list>
+    } @else {
+        No any result.
+    }
+} @else {
+    No any result.
+}