Update prometheus.md with proper dockerfile label syntax (#23948)

Author: sam-muldrow

content/en/containers/docker/prometheus.md

@@ -86,15 +86,15 @@ The Agent detects if it's running on Docker and automatically searches all conta
 ```conf
 LABEL "com.datadoghq.ad.check_names"='["openmetrics"]'
 LABEL "com.datadoghq.ad.init_configs"='[{}]'
-LABEL "com.datadoghq.ad.instances"='["{\"openmetrics_endpoint\":\"http://%%host%%:<PROMETHEUS_PORT>/<PROMETHEUS_ENDPOINT> \",\"namespace\":\"<NAMESPACE>\",\"metrics\":[{\"<METRIC_TO_FETCH>\": \"<NEW_METRIC_NAME>\"}]}"]'
+LABEL "com.datadoghq.ad.instances"='[{"openmetrics_endpoint":"http://%%host%%:<PROMETHEUS_PORT>/<PROMETHEUS_ENDPOINT>","namespace":"<NAMESPACE>","metrics":[{"<METRIC_TO_FETCH>": "<NEW_METRIC_NAME>"}]}]'
 ```
 
 #### Multiple endpoints example
 
 ```conf
 LABEL "com.datadoghq.ad.check_names"='["openmetrics","openmetrics"]'
 LABEL "com.datadoghq.ad.init_configs"='[{},{}]'
-LABEL "com.datadoghq.ad.instances"='["{\"openmetrics_endpoint\":\"http://%%host%%:<PROMETHEUS_PORT>/<PROMETHEUS_ENDPOINT> \",\"namespace\":\"<NAMESPACE>\",\"metrics\":[{\"<METRIC_TO_FETCH>\": \"<NEW_METRIC_NAME>\"}]}", "{\"openmetrics_endpoint\":\"http://%%host%%:<PROMETHEUS_PORT>/<PROMETHEUS_ENDPOINT> \",\"namespace\":\"<NAMESPACE>\",\"metrics\":[{\"<METRIC_TO_FETCH>\": \"<NEW_METRIC_NAME>\"}]}"]'
+LABEL "com.datadoghq.ad.instances"='[{"openmetrics_endpoint":"http://%%host%%:<PROMETHEUS_PORT>/<PROMETHEUS_ENDPOINT>","namespace":"<NAMESPACE>","metrics":[{"<METRIC_TO_FETCH>": "<NEW_METRIC_NAME>"}]}, {"openmetrics_endpoint":"http://%%host%%:<PROMETHEUS_PORT>/<PROMETHEUS_ENDPOINT>","namespace":"<NAMESPACE>","metrics":[{"<METRIC_TO_FETCH>": "<NEW_METRIC_NAME>"}]}]'
 ```
 
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