dot/rpc: implement RPC call state_control

[edwardmack]

Changes

Introduce RPC method to control services

• There is currently in issue when calling stop on babe, it cause the node to crash with a panic because sendVoteMessages tries to send on a closed channel:

panic: send on closed channel

goroutine 76 [running]:
github.com/ChainSafe/gossamer/dot/core.(*Service).sendVoteMessages(0xc0002aa1e0)
        /home/emack/projects/chainsafe/gossamer/dot/core/finality.go:49 +0x207
created by github.com/ChainSafe/gossamer/dot/core.(*Service).Start
        /home/emack/projects/chainsafe/gossamer/dot/core/service.go:234 +0x219

Process finished with exit code 2

• Call RPC method state_control and params array of strings where first element is service (currently babe or network), second element command (start or stop).
• it returns an error if the service returns an error.

Tests:

Start gossamer with rpc

./bin/gossamer --key alice --rpc

Make RPC call (example to stop babe service):

curl --location --request POST 'http://127.0.0.1:8545' --header 'Content-Type: application/json' --data-raw '{
    "jsonrpc": "2.0",
    "method": "state_control",
    "params": ["babe", "stop"],
    "id": 1
}'

Checklist:

• I have read CONTRIBUTING and CODE_OF_CONDUCT
• I have provided as much information as possible and necessary
• I have reviewed my own pull request before requesting a review
• I have linked any relevant issues in my pull request comments
• All integration tests and required coverage checks are passing

Issues:

• closes Developer RPC Endpoint: Start & stop libp2p network  #855
• closes Developer RPC Endpoint: Start & stop block production  #856

[noot]

@edwardmack I updated this to have a RPC dev module that directly uses the BlockProducer interface. it looks like it works now:

./bin/gossamer --key alice --rpc --rpcmods="dev" 

then:

$ curl --location --request POST 'http://127.0.0.1:8545' --header 'Content-Type: application/json' --data-raw '{
    "jsonrpc": "2.0",
    "method": "dev_control",
    "params": ["babe", "start"],
    "id": 1
}'

I'm wondering whether we should have separate calls for BABE and network (and start and stop), what do you think? it works as is so not a huge deal.

[edwardmack]

@noot, this looks great, it makes sense to use the BlockProducer interface. Regarding call format, I'm open. I could create a call to start and one to stop, and pass in babe or network (and possible future things). OR I could do a call for babe and on for network, and pass in start or stop. I'm open, let me know.

[noot]

@edwardmack let's leave it for now, in the future if we add more services to control it might make more sense to break it out. but I think it's fine as is