Add submit button component and style it.

frontend/src/app/components/submit-button/submit-button.component.html

@@ -0,0 +1,8 @@
+<button type="submit" [class]="color" [disabled]="disabled || requestPending" (click)="click.emit()">
+    @if (requestPending) {
+        <mat-spinner class="spinner {{color}}" [diameter]="25"></mat-spinner>
+    }
+    <span>
+        {{ label }}
+    </span>
+</button>