Cucumber tests for `min-balance`

[tzaffi]

Introduction

https://github.com/algorand/go-algorand/pull/3287 has introduced min-balance to the response of algod's /v2/accounts/{{ACCOUNT}} as well as to the goal account info. "For free", it is also introduced into the Python SDK's account_info() method. We'll need to implement this functionality in all our other SDK's. To ensure that the SDK's behave as expected, we should adhere to a spec that is defined in a cucumber test.

part of: https://github.com/algorand/indexer/issues/808

Output

1. Cucumber test that describes what the min-balance field should look like when calling account_info()
2. Issues for implementing the feature and passing tests in each of the 4 SDK's