chg name and type to string from img path

gfl-plugin/src/main/resources/gfl-indexer.xslt

@@ -659,7 +659,7 @@ Refer to comments in the code to understand the used algorithm.
                   </field>
                <!-- give me image contains var id -->
                <xsl:variable name="clean_image_id" select="substring($image_id, 2)"/>
-                  <field name="image_urls">
+                  <field name="image_url">
                      <xsl:value-of select="img:get_path($clean_image_id, $context)"/>
                  </field> 
                </xsl:if>    

solr/gfl/conf/schema.xml

@@ -95,7 +95,7 @@
    <field name="html_page" type="text_de" multiValued="false" />
    <field name="image_ids" type="string" multiValued="true"/>
    <field name="image_urls" type="string" multiValued="true"/>
- 
+   <field name="image_url" type="string" mulitValued="false" />
    
    <!-- for doctype 'article' -->
   <field name="number_of_pages" type="int" />