[EPIC] Handling multi-thread issues in Graviton

[jerryshao]

Describe the proposal

Currently, we lack multi-thread support in Graviton, which may lead to several issues, for example:

1. During catalog operations, we may face contention issues when manipulating both the underlying sources and Graviton store.
2. When several metadata manipulation operations issue simultaneously on the same metadata object.
3. When the system is in starting or stopping period, how to handle the incoming requests.

There might be several different corner cases with this multi-threading issue. So we should have a thorough solution to handle all the cases.

Task list

• Introduce the fine-grained tree lock structure. #778
• Update the current lock to use this tree lock #779
• Remove the lock mechanism in RocksDB #780
• Introduce the state machine mechanism