Add the ability to adjust the `GOGC` variable from the Prometheus
configuration file.
* Create a new top-level `runtime` section in the config.
* Adjust from the Go default of 100 to 50 to reduce wasted memory.
* Use the `GOGC` env value if no configuraiton is used.
Signed-off-by: SuperQ <superq@gmail.com>
This also fixes a bug in query_log_file, which now is relative to the config file like all other paths.
Signed-off-by: Andy Bursavich <abursavich@gmail.com>