Add visibility to postgresql logs from yb-tserver /utilz

[ajcaldera1]

Jira Link: DB-2370
As a user, it would be helpful to have access to the current postgresql-yyyy-mm-dd_hhmmss.log similar to the INFO log for yb-tserver on the yb-tserver:9000/utilz page.
Often in support situations we need to see what messages are being generated in the postgres log to properly diagnose what the issue is, and having visibility from the tserver web-ui would aid in this. Right now, we have to walk the user through going to the specific log location and sending it to us.