* fix broken links for the v2 branch

v2 brach has broken links to read the docs too

I additionally found a link to the git hub master tree, which should be
changed to main.

* #1295 github link fixed (master->v2)

Co-authored-by: Peter Paul Kiefer <dafisppk@gmail.com>

* fixed broken links to graphene filter documentation (master->main)

* #1295 There is still a wrong link to github

The referenced example is in main branch
but the link goes to the master branch which still exists.

Co-authored-by: Peter Paul Kiefer <dafisppk@gmail.com>