feat: Init logger, add initial MemDB plugin

[erezrokah]

Beginning of #5.

Started implementing a MemDB plugin, but other things got in the way:

1. Dropped the plugin builder as it makes it harder to extend it (I found https://projectlombok.org/features/experimental/SuperBuilder but didn't dig deeper)
2. Looks like we shouldn't throw in the serve command so the caller can use the return value and do System.exit(exitCode)
3. Removed the docs command as now the CLI does it
4. Initialized the logger via code using log4j2 (couldn't find an easier way to support JSON logging)

[mnorbury]

Looks good

[mnorbury]

1. Dropped the plugin builder as it makes it harder to extend it (I found https://projectlombok.org/features/experimental/SuperBuilder but didn't dig deeper)

Good call with the Plugin builder. I think that class makes more sense as an abstract class.