feat: add flags to write json logs, to set log level

[burningalchemist]

These flags refer to go-kit/log, which seems to become our replacement for klog.

• -log.json - to write logs in JSON instead of logfmt;
• -log.level - to set log level (currently debug by default, as we use klog-gokit bridge).

[jakob-reesalu]

@burningalchemist Something wrong here, when trying to set log level:
.\sql_exporter.exe -log.level debug

I get this:
flag provided but not defined: -log

[burningalchemist]

Hey @jakob-reesalu, it seems that the dot character is omitted as it might be intercepted by the interpreter on Windows. Are you running the command from CMD or from Powershell? Could you try to write the flag with double dash in front like --log.level?

[jakob-reesalu]

Oh, that worked! Great! Thanks!