Implement a non-volatile SecondaryCache

RocksDB added support for a SecondaryCache in #8271, #8191 and #8312. The SecondaryCache is an additional tier of caching below the block cache. It can be used to provide a non-volatile cache tier on local flash or NVM/SCM that can complement the DRAM block cache. More details about the design of SecondaryCache can be found [here](https://rocksdb.org/blog/2021/05/27/rocksdb-secondary-cache.html).

We are looking for a community contribution of SecondaryCache implementations, which would make this feature usable by the broader RocksDB userbase.