[IMP] mass_mailing_themes: replace theme_tech static image with shape

This theme was using a static image which was designed in a triangle
shape but could not be edited with the `Shapes` option.

In order for the user to be able to change the shape of this image,
much like in the previous commit, a square version of the image is used
as an `original-src`, and the triangle version of it is used as `src`
in the theme.

task-2836942

Part-of: odoo/odoo#95974

addons/mass_mailing_themes/views/mass_mailing_themes_templates.xml

@@ -217,7 +217,7 @@
                         <div style="text-align:left;"><a class="btn btn-primary rounded-circle" href="#">VISIT OUR WEBSITE</a></div>
                     </div>
                     <div class="col-lg-5 px-0">
-                        <img src="/mass_mailing_themes/static/src/img/theme_tech/tech_banner_image.jpg" class="img w-100"/>
+                        <img class="img-fluid o_we_custom_image" src="/mass_mailing_themes/static/src/img/theme_tech/text_image-triangle.png" data-original-id="242" data-original-src="/mass_mailing_themes/static/src/img/theme_tech/s_default_image_text_image.jpg" data-mimetype="image/svg+xml" data-shape="mass_mailing/basic/triangle" data-file-name="text_image-triangle.svg" data-shape-colors=";;;;" data-original-mimetype="image/jpeg"/>
                     </div>
                 </div>
             </div>