Support advanced zap configuration

[maxime1907]

Is your feature request related to a problem? Please describe.
We are using goldpinger on our self hosted kubernetes clusters with fluentd to gather logs into our elasticsearch but the thing is that its not possible to adjust the logger configuration such as the level since its hardcoded thus leaving us with a lot of logs ingested that costs us a certain amount of money.

Describe the solution you'd like
Implement a way to load a custom zap configuration through a json file as its described in their official documentation

Describe alternatives you've considered
Implement command line arguments to configure each component of zap like --zap-level but it will be more work to maintain the link between command line arguments and zap's expected parameters:

• What if they remove/change the name of one of their config variable?