Make log viewer timezone-aware

[erickzhao]

Problem statement

Sleuth displays log files in a tabular format using the @blueprintjs/table library. Each line in the table has a timestamp corresponding to the time on the user's system.

Separately, our logs also ship a log-context.json file that specify the user's timezone:

{
  "systemTZ": "America/New_York"
}

It would be useful for Sleuth to have a toggle that can switch the log timestamps from the user's TZ to the sleuth's TZ.