Docs: how to avoid reading /var/log/btmp on each SSH login without causing security concerns for non-git traffic

#350463 (comment 818555339) found that each SSH login read /var/log/btmp when UsePAM is enabled in sshd_config which when large can spike the CPU load.

!78955 (merged) introduces troubleshooting details. How can this issue be solved for systems that need UsePAM enabled?