Migrate Avro message converter artifacts

Migrate Avro message converter (non-schema-registry) artifacts
from Spring Cloud Schema Registry to Spring Cloud Function.

Resolves https://github.com/spring-cloud/spring-cloud-function/issues/732
Resolves #733

spring-cloud-function-context/src/test/resources/avro/sensor.avsc

@@ -0,0 +1,11 @@
+{
+  "namespace" : "com.example",
+  "type" : "record",
+  "name" : "Sensor",
+  "fields" : [
+    {"name":"id","type":"string"},
+    {"name":"temperature", "type":"float", "default":0.0},
+    {"name":"acceleration", "type":"float","default":0.0},
+    {"name":"velocity","type":"float","default":0.0}
+  ]
+}