Implement interface to report capabilities

Configuration options, such as whether volume support is enabled should be available via the trove API to enable projects building on top of Trove, viz., Horizon. In the case of volume support, it would be possible to have two backends one supporting different DBs and different configurations for volume support. To be able to guide the user to the required options knowing the capabilities of the backend is essential, otherwise the user is left to guess and hopefully succeed through trial and error.