Added /findDistrict to api docs; optimized findDistrict query

public/docs/preorder-api.yaml

@@ -203,6 +203,48 @@ paths:
             Parameter missing or malformed
         '401':
           description: Unauthorized
+  /addressdb/findDistrict:
+    get:
+      tags:
+        - addressdb
+      summary: Ortsteile suchen
+      description: Sucht nach Ortsteilen
+      operationId: findDistrict
+      parameters:
+        - name: zip
+          description: Postleitzahl Suchbegriff
+          in: query
+          schema:
+            type: string
+        - name: city
+          description: Gemeinde Suchbegriff
+          in: query
+          schema:
+            type: string
+      responses:
+        '200':
+          description: Successful operation
+          content:
+            application/json:
+              schema:
+                type: object
+                properties:
+                  status:
+                    type: string
+                    description: Status string
+                    example: OK
+                  result:
+                    type: object
+                    properties:
+                      cities:
+                        $ref: '#/components/schemas/CityDistricts'
+        '400':
+          description: |
+            Bad Request
+            
+            Parameter missing or malformed
+        '401':
+          description: Unauthorized
   /preorder:
     post:
       tags:
@@ -360,6 +402,18 @@ components:
       type: array
       items:
         type: string
+    CityDistricts:
+      type: object
+      additionalProperties:
+        type: array
+        items:
+          type: string
+      example:
+        Premstätten:
+          - Hautzendorf
+          - Laa
+          - Oberpremstätten
+          - Unterpremstätten
     Streets:
       type: array
       items: