Add kairos server test hook

[marijanp]

No description provided.

[koxu1996]

Comment: This is not a graceful shutdown, but for testing it seems to be okay.

[koxu1996]

Comment: In the future we should introduce healtcheck mechanism - for example /health endpoint - because open port does not mean that server is ready to process requests.

[koxu1996]

Please go back to stable Rust, then I have no other concerns about this PR.

[github-actions]

File	Coverage
All files	65%	✅
kairos-tx/src/asn.rs	77%	✅
kairos-tx/src/error.rs	0%	❌
kairos-server/src/config.rs	0%	❌
kairos-server/src/errors.rs	16%	❌
kairos-server/src/utils.rs	22%	❌
kairos-server/src/routes/deposit.rs	86%	✅
kairos-server/src/routes/transfer.rs	73%	✅
kairos-server/src/routes/withdraw.rs	91%	✅
kairos-crypto/src/implementations/casper.rs	3%	❌
kairos-test-utils/src/cctl/parsers.rs	66%	✅
kairos-test-utils/src/cctl.rs	92%	✅
kairos-test-utils/src/kairos.rs	95%	✅
kairos-server/tests/transactions.rs	83%	✅

Minimum allowed coverage is 60%

Generated by 🐒 cobertura-action against 6ffd7a9