add feature 'integration-test' for full-flegded tests that use postgr…

[grooviegermanikus]

Run it with this command

RUST_LOG=info,blockstore_integration_tests=trace,solana_lite_rpc_blockstore=trace RUST_LOG=info,blockstore_integration_tests=trace,solana_lite_rpc_blockstore=trace RPC_ADDR=https://api.testnet.rpcpool.com/$TESTNET_API_TOKEN WS_ADDR=wss://api.testnet.rpcpool.com/$TESTNET_API_TOKEN GRPC_ADDR=https://api.testnet.rpcpool.com/ GRPC_X_TOKEN=$TESTNET_API_TOKEN cargo test -F integration-test --test blockstore_integration_tests

SQL Script to prepare local PostgreSQL can be found in localdev_integrationtest.sql