Azure OpenAI magics, support for provider fields in magics

[dlqqq]

Problem

Right now, there is no general way of providing a field value declared in Provider.fields to a provider via magics. For providers that do require fields, like SageMaker Endpoints, we have to explicitly add a keyword argument for each field we want to support via magics.

This strategy grows increasing untenable as we add more providers with more fields. For example, #322 adds various fields that do not have a corresponding magics implementation.

Proposed Solution

We need to have the magics automatically read from Provider.fields and allow for field values to be passed via magics arguments. There are various ways to implement this; perhaps each Provider declares a magics parser instance as an attribute, and the magics uses each provider's corresponding parser in addition to its own?