Added two new auth interfaces

Author: artem-v

services-api/src/main/java/io/scalecube/services/auth/CredentialsSupplier.java

@@ -0,0 +1,9 @@
+package io.scalecube.services.auth;
+
+import java.util.Map;
+import reactor.core.publisher.Mono;
+
+public interface CredentialsSupplier {
+
+  Mono<Map<String, String>> credentials(Map<String, String> tags);
+}

services-api/src/main/java/io/scalecube/services/auth/CredentialsSuppliers.java

@@ -0,0 +1,6 @@
+package io.scalecube.services.auth;
+
+public interface CredentialsSuppliers {
+
+  CredentialsSupplier forServiceRole(String serviceRole);
+}