Migrate PBS container to rocklinux 8 and openpbs 23.06

[jacobtomlinson]

Current builds of the PBS container are failing due to centos being EOL. I migrated the container to rockylinux 8.

It also seems that PBS Pro Open Source has been renamed to openpbs. They also provide rpms for rockylinux 8 so I simplified the build to just download and install those artifacts.

I tested this locally by running ci/pbs/start-pbs.sh after building.

$ cd ci/pbs/start-pbs
$ cp ../environment.yaml .
$ docker compose build
...
$ ./start-pbs.sh
[+] Running 6/6
 ✔ Network pbs_default        Created                                                                                                                                                      0.1s 
 ✔ Volume "pbs_userhome"      Created                                                                                                                                                      0.0s 
 ✔ Volume "pbs_shared_space"  Created                                                                                                                                                      0.0s 
 ✔ Container pbs_master       Started                                                                                                                                                      0.1s 
 ✔ Container pbs_slave_2      Started                                                                                                                                                      0.1s 
 ✔ Container pbs_slave_1      Started                                                                                                                                                      0.1s 
Waiting for PBS slave nodes to become available
Waiting for PBS slave nodes to become available
Waiting for PBS slave nodes to become available
PBS properly configured

[jacobtomlinson]

Build is passing so I'm going to go ahead and merge this in.