Improve documentation of `fields` arguments

[thomsentner]

Is your feature request related to a problem? Please describe. Currently, it's quite unclear which arguments are accepted by which flask_restx.fields functions. For example, for fields.Float, none are explicitly documented. To find out how to specify exclusiveMinimum, I have to read the source code of fields.Float, which inherits fields.NumberMixin, which inherits fields.MinMaxMixin, where I finally find out that an openAPI exclusiveMinimum is specified with the RestX argument exclusiveMin.

Describe the solution you'd like Improved documentation or code changes. Really any improvement would be welcome.