Q3 MBO - Implement My organisation is ready to join flow

On https://www.eclipse.org/org/workinggroups/explore.php, we have a button on each WG with the label "My organization is ready to join".

That link should redirect the users to the correct location. For example, we need to ask them to log in and if we detect they work for an existing member organization, we must redirect them to the WG form within the member portal. If they are not working for an existing Eclipse Member, we must redirect them to our membership application form.

This is the original design from Marketing: https://xd.adobe.com/view/07c1240b-f2de-46cc-bbbf-01219612b44d-5292/

This was initially requested by @sgiacomoni2as: #638 (comment 2085629)

I am creating this issue to track this since I am making this a Q3 MBO for webdev.