Tenets:
1. Limit thread names to 15 characters
2. Prefix all Solana-controlled threads with "sol"
3. Use Camel case. It's more character dense than Snake or Kebab case
* Add BlockHeight CF to blockstore
* Rename CacheBlockTimeService to be more general
* Cache block-height using service
* Fixup previous proto mishandling
* Add block_height to block structs
* Add block-height to solana block
* Fallback to BankForks if block time or block height are not yet written to Blockstore
* Add docs
* Review comments