Add Casper RPC url to server configuration

[koxu1996]

This PR adds Casper RPC configuration to kairos-server:

#[derive(Debug)]
pub struct ServerConfig {
    pub socket_addr: SocketAddr,
+    pub casper_rpc: Url,
}

Notably, it is common requirement among 2 PRs:

• https://github.com/cspr-rad/kairos/pull/96
• https://github.com/cspr-rad/kairos/pull/94

[github-actions[bot]]

File	Coverage
All files	53%	:x:
kairos-test-utils/src/cctl/parsers.rs	66%	:white_check_mark:
kairos-server/src/routes/deposit.rs	88%	:white_check_mark:
kairos-server/src/routes/transfer.rs	90%	:white_check_mark:
kairos-test-utils/src/cctl.rs	87%	:white_check_mark:
kairos-crypto/src/implementations/casper.rs	6%	:x:
kairos-tx/src/asn.rs	48%	:x:
kairos-tx/src/error.rs	0%	:x:
kairos-server/src/config.rs	0%	:x:
kairos-server/src/errors.rs	12%	:x:
kairos-server/src/lib.rs	95%	:white_check_mark:
kairos-server/src/state.rs	90%	:white_check_mark:
kairos-server/src/utils.rs	22%	:x:
kairos-server/tests/transactions.rs	85%	:white_check_mark:
kairos-server/src/state/transactions.rs	57%	:x:
kairos-server/src/state/trie.rs	35%	:x:
kairos-server/src/state/transactions/batch_state.rs	40%	:x:

Minimum allowed coverage is 60%

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