support-policy section was renamed in
- https://review.opendev.org/#/c/725446/

but redirect for that was not correct. Fixing that
redirect.

Change-Id: Ia2921533c7a61bab4325a4a89b2b84f391e0aafd

Now we have more documents for plugins on stable release,
support and their testing policy. Let's prepare a
index page for it will be easy for plugins maintainer.

Also renaming the stable support policy section to have a clear
name.

Adding redirect links for moved documents.

Change-Id: I17a9a6e0e88605a0ee5047678d6ed168c31396ec

This commit adds an .htaccess file to the tempest docs to handle
redirecting old paths to the new location. Before the docs migration in
the past we had docs located at docs.openstack.org/developer/tempest and
now things are located in docs.openstack.org/tempest/latest. With this
file we should be properly redirecting old links to the new location.

Change-Id: Idec7b2f299ade9b7dcc678ea1daf8daa25f08c44