Use only public APIs in Go end-to-end tests

**As a** Go contributor
**I want** the end-to-end tests to be implemented using only public APIs
**So that** I can ensure that the fabric-admin-sdk implementation is usable by consuming Go modules

The current end-to-end tests (in the `test` package) are part of the fabric-admin-sdk module and make use of internal packages for their implementation. These tests should ensure that the fabric-admin-sdk module provides end-to-end capability for consuming Go modules. One option to ensuring this is for the end-to-end tests to be defined in their own module so that they accurately reflect the experience of a consuming Go module, although this is not strictly necessary.

This change will require some rework of the end-to-end tests (and possibly the fabric-admin-sdk API) to implement the required functionality without accessing internal packages.