Add logger interface

[joshklop]

Problem

Right now, we require the zap logging library directly (transitively requiring all code to use zap for logging as well). Furthermore, we frequently import a global logger rather than passing it as a parameter.

Solution

• A logger interface to decouple Juno from zap
• Pass loggers as parameters to functions and add them to existing structs, rather than importing a global logger. Among other benefits, this allows for greater flexibility in package-level logger configuration.