WIP: Switch to gojsonschema

[fenollp]

Fixes incorrect schema validation:

• Request validation does not work correctly with "additionalProperties: false" #82
• Incorect validation of nullable in allOf #171
• Validating an enum array does not seem to work #203
• formData will not validate schemas with oneOf  #267
• schema of number is float64 #280
• incorrect handling of non-nullable deepObject properties #293

Changes format support:

• Add DefineNumberFormat function #107

Also:

• works towards OpenAPIv3.1

[bhechinger]

What is holding this PR back? I really need kin-openapi to properly validate nullable enums. :(

[fenollp]

@bhechinger From #230 we most probably will move to use https://github.com/qri-io/jsonschema instead of the lib in this PR.

I didn't start work on this yet.. maybe give it a shot?

[bhechinger]

@fenollp I'll take a look. If it's not going to be too much work to get done I may actually be able to make it a pre-req for my current task at work. :)

[bhechinger]

Due to our current timeline crunch I won't have time for this right now. However, I was instructed to open a tech debt ticket to track this and come back to it later. If this hasn't been done by someone else in the next several months I will do it.