[chore][receiver/nginxreceiver] sort metadata.yaml entries (open-telemetry#43477)

#### Description

Sort metadata.yaml file in preparation for sort validation using
mdatagen. Context:
open-telemetry/opentelemetry-collector#13782

Signed-off-by: Paulo Dias <[email protected]>

Author: paulojmdias

receiver/nginxreceiver/metadata.yaml

@@ -14,34 +14,34 @@ attributes:
     description: The state of a connection
     type: string
     enum:
-    - active
-    - reading
-    - writing
-    - waiting
+      - active
+      - reading
+      - writing
+      - waiting
 
 metrics:
-  nginx.requests:
+  nginx.connections_accepted:
     enabled: true
-    description: Total number of requests made to the server since it started
+    description: The total number of accepted client connections
     stability:
       level: development
-    unit: requests
+    unit: connections
     sum:
       value_type: int
       monotonic: true
       aggregation_temporality: cumulative
     attributes: []
-  nginx.connections_accepted:
+  nginx.connections_current:
     enabled: true
-    description: The total number of accepted client connections
+    description: The current number of nginx connections by state
     stability:
       level: development
     unit: connections
     sum:
       value_type: int
-      monotonic: true
+      monotonic: false
       aggregation_temporality: cumulative
-    attributes: []
+    attributes: [state]
   nginx.connections_handled:
     enabled: true
     description: The total number of handled connections. Generally, the parameter value is the same as nginx.connections_accepted unless some resource limits have been reached (for example, the worker_connections limit).
@@ -53,14 +53,14 @@ metrics:
       monotonic: true
       aggregation_temporality: cumulative
     attributes: []
-  nginx.connections_current:
+  nginx.requests:
     enabled: true
-    description: The current number of nginx connections by state
+    description: Total number of requests made to the server since it started
     stability:
       level: development
-    unit: connections
+    unit: requests
     sum:
       value_type: int
-      monotonic: false
+      monotonic: true
       aggregation_temporality: cumulative
-    attributes: [state]
+    attributes: []