Fix config prop name in gRPC client and server

The config prop name was mismatched in the both the gRPC client
and server modules additional-spring-configuration-metadata.json
files. This makes them consistent using the singular form of the
property `spring.grpc.(client|server).observation.enabled`.

Signed-off-by: onobc <chris.bono@gmail.com>

Author: onobc

module/spring-boot-grpc-client/src/main/resources/META-INF/additional-spring-configuration-metadata.json

@@ -20,7 +20,7 @@
       "defaultValue": true
     },
     {
-      "name": "spring.grpc.client.observations.enabled",
+      "name": "spring.grpc.client.observation.enabled",
       "type": "java.lang.Boolean",
       "description": "Whether to enable Observations on the client.",
       "defaultValue": true

module/spring-boot-grpc-server/src/main/resources/META-INF/additional-spring-configuration-metadata.json

@@ -20,7 +20,7 @@
       "defaultValue": true
     },
     {
-      "name": "spring.grpc.server.observations.enabled",
+      "name": "spring.grpc.server.observation.enabled",
       "type": "java.lang.Boolean",
       "description": "Whether to enable Observations on the server.",
       "defaultValue": true