Use rockdb instead of leveldb for persistent plugin?

[He-Pin]

(https://github.com/facebook/rocksdb) seems well maintained

[pjfanning]

leveldb support is deprecated and probably should be removed in 2.0.0

pekko/docs/src/main/paradox/persistence-query-leveldb.md

Line 3 in 8534c91

The LevelDB journal and query plugin is deprecated and it is not advised to build new applications with it.

I'm not sure that we need to support rocksdb. Maybe if people request it or donate an impl, we could create a separate repo like the way we have 4 pekko-persistence-* repos and some community ones too.