Update Interest Group widget to use membership API to fetch organizations

In the Interest Group members widget (https://gitlab.eclipse.org/eclipsefdn/it/webdev/solstice-assets/-/blob/main/js/api/eclipsefdn.interest-groups.js), we currently fetch the interest group from the projects API, then iterate over each to extract organizations from the members then individually call for each organization. There is a better solution to this that uses the following endpoint as an example https://membership.eclipse.org/api/interest_groups/31984/organizations, where 31984 is the nid of one of the interest groups.

I plan on making a change to the Membership API to change the underscore in the above API to a dash. This widget was meant to be the main consumer of that endpoint, so this will be a safe breaking change.