Add verbosity_map and integer timestamp example

since rabbitmq/rabbitmq-server#3281 and
rabbitmq/rabbitmq-server#3283 are merged.

Example log output:
{"v":7,"time":1629703633887530,"msg":"accepting AMQP connection <0.1321.0> (10.244.0.1:43532 -> 10.244.0.14:5672)","domain":"rabbitmq.connection","pid":"<0.1321.0>","gl":"<0.223.0>"}

docs/examples/json-log/README.md

@@ -6,7 +6,7 @@ Pull Requests:
 * [Switch from Lager to the new Erlang Logger API for logging #2861](https://github.com/rabbitmq/rabbitmq-server/pull/2861)
 * [Logging: Add configuration variables to set various formats #2927](https://github.com/rabbitmq/rabbitmq-server/pull/2927)
 
-This example configures RabbitMQ to output JSON logs.
+This example (requiring RabbitMQ >= v3.9.3) configures RabbitMQ to output JSON logs.
 
 You can deploy this example like this:
 

docs/examples/json-log/rabbitmq.yaml

@@ -16,5 +16,6 @@ spec:
       log.console = true
       log.console.level = debug
       log.console.formatter = json
-      log.console.formatter.json.field_map = level time msg domain file line pid
-      log.console.formatter.time_format = rfc3339_T
+      log.console.formatter.json.field_map = verbosity:v time msg domain file line pid level:-
+      log.console.formatter.json.verbosity_map = debug:7 info:6 notice:5 warning:4 error:3 critical:2 alert:1 emergency:0
+      log.console.formatter.time_format = epoch_usecs