🔒️ Use keyring to store random private key

[BertrandD]

The private key is randomly generated & stored given the validator name
We can set the private key using an hex string in an env var (meant for
kubernetes setup using kube secrets)

In testing env, the private keys are deterministically generated from
the validator name, to keep same behavior as before.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

✅ All tests successful. No failed tests found.

Files with missing lines	Coverage Δ
src/consensus.rs	84.00% <100.00%> (ø)
src/genesis.rs	95.19% <100.00%> (ø)
src/mempool.rs	86.81% <100.00%> (ø)
src/mempool/storage.rs	74.94% <ø> (ø)
src/single_node_consensus.rs	74.69% <100.00%> (ø)
src/utils/crypto.rs	99.63% <100.00%> (+<0.01%)	⬆️
src/utils/integration_test.rs	92.92% <100.00%> (ø)

[maxgttph]

👍