feat: generate enums as integer types

[m-kay]

Add 2 new options for generating protobuf enums as integer types.

1. use_int_enums=true: generates enums as type: integer with the respective protobuf numbers
2. enum_names_extensions=x-enumNames;x-enum-varnames: generates extensions in the enums with the names of enums used for the openapi generators to generate better enums.

[solo-build-bot]

Waiting for approval from someone in the solo-io org to start testing.

[m-kay]

@sam-heilbron Any chance you could have a look at this?