feat: implement e2e-tests crate and kv-store example

[fbozic]

Asserting/expecting turned out to be a bad idea since I can not handle node stop properly. I will fix that in the follow-up PR.
The output format can be also improved massively.

Failing tests example:

❯ cargo run -p e2e-tests -- --input-dir ./e2e-tests/config --output-dir ./e2e-tests/corpus --merod-binary ./target/debug/merod --meroctl-binary ./target/debug/meroctl
Running command './target/debug/merod' ["--home", "./e2e-tests/corpus/nodes", "--node-name", "node1", "init", "--swarm-port", "2427", "--server-port", "2527"]
Running command './target/debug/merod' ["--home", "./e2e-tests/corpus/nodes", "--node-name", "node1", "run"]
Running command './target/debug/merod' ["--home", "./e2e-tests/corpus/nodes", "--node-name", "node2", "init", "--swarm-port", "2428", "--server-port", "2528"]
Running command './target/debug/merod' ["--home", "./e2e-tests/corpus/nodes", "--node-name", "node2", "run"]
Loaded test scenario from file: "./e2e-tests/config/scenarios/kv-store/test.json"
TestScenario { steps: [ContextCreate(CreateContextStep { application: LocalFile("./apps/kv-store/res/kv_store.wasm") }), JsonRpcExecute(JsonRpcExecuteStep { method_name: "set", args_json: Object {"key": String("foo"), "value": String("bar")}, expected_result_json: None }), JsonRpcExecute(JsonRpcExecuteStep { method_name: "get", args_json: Object {"key": String("foo")}, expected_result_json: Some(String("baz")) }), ContextInviteJoin(InviteJoinContextStep)] }
================= Starting step =================
Step: ContextCreate(CreateContextStep { application: LocalFile("./apps/kv-store/res/kv_store.wasm") })
Running command './target/debug/meroctl' ["--home", "./e2e-tests/corpus/nodes", "--node-name", "node1", "--output-format", "json", "app", "install", "--path", "./apps/kv-store/res/kv_store.wasm"]
Running command './target/debug/meroctl' ["--home", "./e2e-tests/corpus/nodes", "--node-name", "node1", "--output-format", "json", "context", "create", "-a", "BA8iKev6bGA3nedpnGDQvZFzhsK18QoAauDnk8Q4hJDL"]
================= Finished step =================
================= Starting step =================
Step: JsonRpcExecute(JsonRpcExecuteStep { method_name: "set", args_json: Object {"key": String("foo"), "value": String("bar")}, expected_result_json: None })
Running command './target/debug/meroctl' ["--home", "./e2e-tests/corpus/nodes", "--node-name", "node1", "--output-format", "json", "json-rpc", "3eLoXVo4U2QtWr6cPMmdRK2xnQmJPn8dR8LbMAkGjnem", "set", "--args-json", "{\"key\":\"foo\",\"value\":\"bar\"}"]
================= Finished step =================
================= Starting step =================
Step: JsonRpcExecute(JsonRpcExecuteStep { method_name: "get", args_json: Object {"key": String("foo")}, expected_result_json: Some(String("baz")) })
Running command './target/debug/meroctl' ["--home", "./e2e-tests/corpus/nodes", "--node-name", "node1", "--output-format", "json", "json-rpc", "3eLoXVo4U2QtWr6cPMmdRK2xnQmJPn8dR8LbMAkGjnem", "get", "--args-json", "{\"key\":\"foo\"}"]
Error: JSON RPC result output mismatch:
expected: "baz"
actual  : "bar"

Location:
    e2e-tests/src/steps/jsonrpc_execute.rs:38:17

[miraclx]

Child::kill?

[fbozic]

I've tried that initially but the node doesn't exit gracefully and we get a broken pipe error.