[#414] ir/control: Implement service server

Implement `ControlServiceServer` on `Server` type. The `Server` requires all
requests to be signed with keys from the so-called whitelist. To obtain
health status, it uses the abstraction in the form of `HealthChecker`
interface.

Signed-off-by: Leonard Lyubich <leonard@nspcc.ru>

pkg/services/control/ir/server/opts.go

@@ -0,0 +1,20 @@
+package control
+
+// Option specifies Server's optional parameter.
+type Option func(*options)
+
+type options struct {
+	allowedKeys [][]byte
+}
+
+func defaultOptions() *options {
+	return new(options)
+}
+
+// WithAllowedKeys returns option to add public keys
+// to white list of the Control service.
+func WithAllowedKeys(keys [][]byte) Option {
+	return func(o *options) {
+		o.allowedKeys = append(o.allowedKeys, keys...)
+	}
+}