Add package-info files for observability packages

Author: acogoluegnes

src/main/java/com/rabbitmq/client/observation/micrometer/package-info.java

@@ -0,0 +1,4 @@
+/**
+ * Micrometer-based observability implementation.
+ */
+package com.rabbitmq.client.observation.micrometer;

src/main/java/com/rabbitmq/client/observation/package-info.java

@@ -0,0 +1,4 @@
+/**
+ * Observability abstractions.
+ */
+package com.rabbitmq.client.observation;