Add routes for fetching category info from titles

app/src/main/java/fr/free/nrw/commons/category/CategoryClient.kt

@@ -78,6 +78,24 @@ class CategoryClient
                 ),
             )
 
+        /**
+         * Fetches categories belonging to an image (P18 of some wikidata entity).
+         *
+         * @param image P18 of some wikidata entity
+         * @param itemLimit How many categories to return
+         * @return Single Observable emitting the list of categories
+         */
+        fun getCategoriesOfImage(
+            image: String,
+            itemLimit: Int,
+        ): Single<List<CategoryItem>> =
+            responseMapper(
+                categoryInterface.getCategoriesByTitles(
+                    "File:${image}",
+                    itemLimit,
+                ),
+            )
+
         /**
          * The method takes categoryName as input and returns a List of Subcategories
          * It uses the generator query API to get the subcategories in a category, 500 at a time.

app/src/main/java/fr/free/nrw/commons/category/CategoryInterface.kt

@@ -61,6 +61,21 @@ interface CategoryInterface {
         @Query("gacoffset") offset: Int,
     ): Single<MwQueryResponse>
 
+    /**
+     * Fetches non-hidden categories by titles.
+     *
+     * @param titles titles to fetch categories for (e.g. File:<P18 of a wikidata entity>)
+     * @param itemLimit How many categories to return
+     * @return MwQueryResponse
+     */
+    @GET(
+        "w/api.php?action=query&format=json&formatversion=2&generator=categories&prop=categoryinfo|description|pageimages&piprop=thumbnail&pithumbsize=70&gclshow=!hidden",
+    )
+    fun getCategoriesByTitles(
+        @Query("titles") titles: String?,
+        @Query("gcllimit") itemLimit: Int,
+    ): Single<MwQueryResponse>
+
     @GET("w/api.php?action=query&format=json&formatversion=2&generator=categorymembers&gcmtype=subcat&prop=info&gcmlimit=50")
     fun getSubCategoryList(
         @Query("gcmtitle") categoryName: String,