Add support for 'float' type in schemas

[przemyslaw-dobrowolski-cl]

According to documentation:
http://gohan.cloudwan.io/gohan/schema.html?highlight=number#type-integer-or-type-number
there is no support for floating-point types. This is problematic if one needs to convert schema
to an openapi file which supports floats. Also, floating-point types are simply useful in some scenarios.