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 +1,23 @@
+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 information about all instances.
+  rpc GetInfo(GetInfoRequest) returns (GetInfoResponse) {}
+}
+
+// Get information about all instances.
+
+message GetInfoRequest {}
+
+message GetInfoResponse {
+  // Error information. Set only on failure.
+  Error error = 1;
+  // Information of instances.
+  Value info = 2;
+}