Fix broken link in SSH and sudo documentation

[jackap]

Expected Behavior

Link redirecting to PAM module to add in linux works and I can read it

Actual Behavior

The link is broken

Steps to Reproduce the Problem

I want to get information about ssh and sudo integration within opa.

1. I go to https://www.openpolicyagent.org/docs/latest/ssh-and-sudo-authorization/
2. Find the link to get more information about the PAM module that lets opa communicate with linux. 3. I click the link and read the documentation.

Additional Info

[jackap]

Broken link is: https://github.com/open-policy-agent/contrib/tree/master/pam_authz/pam#pull
Correct link should be: https://github.com/open-policy-agent/contrib/tree/master/pam_opa/pam