proto: introduce aeon_internal.proto

This patch adds `aeon_internal.proto` which will be used to implement
the internal RPC.

Author: ImeevMA

aeon_internal.proto

@@ -0,0 +1,47 @@
+syntax = "proto3";
+
+import "aeon_error.proto";
+import "aeon_value.proto";
+
+package aeon;
+
+// Internal API to Aeon - a distributed database based on Tarantool.
+service InternalService {
+  // Get configurations of all instances.
+  rpc GetConfig(GetConfigRequest) returns (GetConfigResponse) {}
+}
+
+// Get configurations of all instances.
+
+// General structure of returned configuration
+message Config {
+  // Structure of configuration of single instance.
+  message Instance {
+    // Name of the instance.
+    string name = 1;
+    // Replicaset of the instance.
+    string replicaset = 2;
+    // Group of the instance.
+    string group = 3;
+    // URI of the instance.
+    Value uri = 4;
+    // Instance roles.
+    repeated string roles = 5;
+  }
+  // The name of the instance that provided this configuration.
+  string name = 1;
+  // The configuration of the "aeon.grpc" role of the instance
+  // that provided the configuration.
+  Value params = 2;
+  // Configurations of all instances.
+  repeated Instance instances = 3;
+}
+
+message GetConfigRequest {}
+
+message GetConfigResponse {
+  // Error information. Set only on failure.
+  Error error = 1;
+  // Configurations of instances.
+  Config config = 2;
+}