Partially addresses #1039.

Context

The work in this issue will make CometBFT use only pebbleDB as database, thus deprecating cometbft-db.
As CometBFT will use the same DB interface that cometbft-db uses, users can provide their own implementation of the interface that uses a different database under the hood. They will, therefore, have to change the config.DefaultDBProvider function to return their implementation instead of our default.

However, we will support and maintain only the pebbleDB implementation of the DB interface that CometBFT will use.

ToDo

• Create internal/storage pkg to port the DB interface and pebbleDB's implementation of it that are currently in cometbft-db.
  • merged with feat(storage): Add package internal/storage #4511
• Add tests for pebble functionalities.
  • DB inteface. Merged with feat(storage): Add unit tests for pebble implementation of DB interface. #4515
  • Batch interface. Merged with feat(storage): Add unit tests for pebble implementation of Batch interface. #4522
  • Iterator interface. Merged: feat(storage): Add unit tests for pebble implementation of Iterator interface. #4530
• Import PrefixDB implementation. Merged: feat(storage): Add PrefixDB to pkg internal/storage #4562
• Remove cometbft-db as a dependency. WIP: build(deps): CometBFT no longer imports cometbft-db #4601
• Remove DBBackend field of config.BaseConfig and from config options in toml. chore: remove db_backend config option and CLI argument #4915
• Remove cometbft-db from cometbft build process. Merged with build(deps): Remove cometbft-db from cometbft build. #4650