Use go-enum for enums types

[maoueh]

This brings Marshalling/Unmarshalling as well as lsit of enum values, validation and other goodies.

Kept backward compatibility of shortcut names, some where removed because now duplicated with generated names.

[maoueh]

Lol oups, just realized the file is actually generated. Seems like it's gonna be hard to offer go-enum support! I initially thought it would have been an easy PR as we uses some of this functionalities currently for validation of arguments (in preparation of replacing firehose internal registry).

@YaroShkvorets Any ideas how we could support go-enum somehow? I checked quicktype quickly, don't think there is anything in there that would help.

I could create a wrapped "generator" where I modify the enums (regex or using Go parser). What do you think?

[YaroShkvorets]

I'm not a Go expert, so whatever you think works best - I'll merge. Preferably so it can be easily re-generated if the schema changes.