[Serve] Limit the lines of output for sky sevre logs

[cblmemo]

For long-running services, the logs could be very long. We should default to show the last n lines of the logs.

Version & Commit info:

• sky -v: PLEASE_FILL_IN
• sky -c: PLEASE_FILL_IN

[clintonruairi]

agreed, would be helpful

[shubhscoder]

@cblmemo I am trying to work contribute to this project and would like to work on this issue. Thanks!