No extensibility points (such as retry policies)

[boylec]

Hey thanks for the SDK its useful, however we are finding several gaps that we'd like to be able to include ourselves such as retry policies and things of that nature.

Any plans for this, or would you be willing to look at a PR contribution to open up some extensibility points?

@kdcllc has a PR out that appears to be a very good start but we'd like to open up access to be able to hook in Polly retry policies maybe as an optional parameter to the TaxJarApi or some such.

Polly in the .NET world is somewhat ubiquitous nowadays for people to implement really effective retry policies and most projects that require resiliency are very likely to already have some set of Polly policy builders and such so we believe this would be a great addition to the TaxJar .NET SDK.