Ubuntu 20.04: Upgrade RocksDB

For the Ubuntu 20.04 version of Plenum, upgrade to RocksDB 5.17, which is the version supported on Ubuntu 20.04; https://packages.ubuntu.com/search?searchon=sourcenames&keywords=rocksdb

Background:

Plenum is currently dependent on RocksDB 5.8.8.
When RocksDB 5.17 is used without any code changes several tests hang due to issues encountered by the code under test with the updated version of RocksDB. See https://github.com/hyperledger/indy-plenum/issues/1546 for additional details.
Therefore updates to the code are required to support RocksDB 5.17
As an interim solution the RocksDB 5.8.8 package built by the Build 3rd Party Dependencies job (of the GHA Workflow) will be used. Refer to https://github.com/hyperledger/indy-plenum/issues/1546#issuecomment-883585912 for details.

hyperledger / indy-plenum