Feature/115 page environment catalogue des probes

Add API RPCs to allow web dev on #115 (closed) :

• rpc ListProbes(ListProbesRequest) returns (ListProbesResponse)

$ curl -s -H "agent:9e82e551-ccee-489a-a4c8-81329e70a8a3" -H "api-key:f90d9d23-b0cf-410a-b1cc-d0f8678f8b8b" -XGET 'http://127.0.0.1:7576/v1/probes' | jq .
{
  "probes": [
    {
      "name": "probes/xUkSnG_BSVCn-AX1khPLYg",
      "probe_name": "ping",
      "display_name": "Ping",
      "description": "ICMP for the masses",
      "parameters": [
        {
          "param_name": "count",
          "type": "int"
        },
        {
          "param_name": "interval",
          "type": "int"
        }
      ]
    }
  ],
  "next_page_token": "AAAAAAAAAAAAAAAAAQAAAA"
}

• rpc ListChecks(ListChecksRequest) returns (ListChecksResponse)

$ curl -s -H "agent:9e82e551-ccee-489a-a4c8-81329e70a8a3" -H "api-key:f90d9d23-b0cf-410a-b1cc-d0f8678f8b8b" -XGET 'http://127.0.0.1:7576/v1/checks/targets/MQF0eIJcRZyEBgG_sdLPWA' | jq .
{
  "checks": [
    {
      "name": "checks/i2QYtZBVSnuXjLhQhuAV6w",
      "target": "targets/MQF0eIJcRZyEBgG_sdLPWA",
      "probe": "probes/xUkSnG_BSVCn-AX1khPLYg",
      "state_definition": "threshold",
      "state_values": "{\"states\": [{\"state\": \"critical\",\"match\": \"any\",\"conditions\": [{\"field\": \"rtt\",\"operator\": \"gt\",\"value\": 2,\"reason\": \"way too high\"},{\"field\": \"rtt\",\"operator\": \"le\",\"value\": 0,\"reason\": \"too small to be true\"}]}]}"
    }
  ],
  "next_page_token": "AAAAAAAAAAAAAAAAAQAAAA"
}

• rpc GetCheck(GetCheckRequest) returns (Check)

$ curl -s -H "agent:9e82e551-ccee-489a-a4c8-81329e70a8a3" -H "api-key:f90d9d23-b0cf-410a-b1cc-d0f8678f8b8b" -XGET 'http://127.0.0.1:7576/v1/checks/i2QYtZBVSnuXjLhQhuAV6w' | jq .
{
  "name": "checks/i2QYtZBVSnuXjLhQhuAV6w",
  "target": "targets/MQF0eIJcRZyEBgG_sdLPWA",
  "probe": "probes/xUkSnG_BSVCn-AX1khPLYg",
  "state_definition": "threshold",
  "state_values": "{\"states\": [{\"state\": \"critical\",\"match\": \"any\",\"conditions\": [{\"field\": \"rtt\",\"operator\": \"gt\",\"value\": 2,\"reason\": \"way too high\"},{\"field\": \"rtt\",\"operator\": \"le\",\"value\": 0,\"reason\": \"too small to be true\"}]}]}"
}