Substrate-based blockchains like Polkadot are becoming increasingly relevant.
However, Cactus lacked tools to support developing Substrate-based connectors,
such as a test ledger.

This commit defines a Substrate test ledger that allows to programmatically instantiate
the Substrate Contracts node template (https://github.com/paritytech/substrate-contracts-node).
Thus, it contains a Dockerfile with the test ledger
and the test-ledger file that contains the execution logic.

Signed-off-by: Rafael Belchior <[email protected]>
Signed-off-by: Catarina Pedreira <[email protected]>
Signed-off-by: Peter Somogyvari <[email protected]>