Loads GFM once for per page

## What does this MR do?

Currently the GFM init code is included every time there is a GFM form on the page. This changes that & only includes in once if any number of GFM forms are on the page.

## What are the relevant issue numbers?

#22827

See merge request !6840
Signed-off-by: Rémy Coutable <remy@rymai.me>