Establish requirements for a single underlying storage engine

[thanethomson]

In order to simplify Tendermint's storage mechanism, we need to first establish what typical usage patterns look like. Given that we intend on offloading event indexing, this effort should focus on understanding and gathering data on what the storage workloads look like for specific use cases. This is a tracking issue for everything that needs to be completed in order to end up with a set of requirements for a database that will serve as Tendermint's storage mechanism.

• Define storage use cases and workloads #9943
• Establish and implement the relevant metrics to understand storage workloads #9773
• Capture Tendermint database requirements #9940