Create plan for e2e/smoke/integration tests

[chelseakomlo]

This involves the following:

1. Creating a list of what features should be tested (i.e, what features we expect working for our first release). These features should be coarse-grained; i.e, can it place a payment? Can it sync testnet? Can it send a shielded transaction? etc.
2. Exploring how these features are executed within zebrad
3. Creating a manual testing plan for these features for the short term (e.g, for integration testing before a release). This involves how to validate whether it succeeded or failed.
4. When we can, these tests should be automated (future work)

Smoke tests in zcashd are a good example of what we want eventually, although these are at the RPC level so miss CLI functionality, which we'll want to test as well: https://github.com/zcash/zcash/tree/master/qa/rpc-tests