DOCSP-42397 add Prometheus user roles info (#327)

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- [DOCSP-42397](https://jira.mongodb.org/browse/DOCSP-42397)
-
[STAGING](https://preview-mongodbkanchanamongodb.gatsbyjs.io/ops-manager/DOCSP-42397/tutorial/prometheus-integration/#enter-your-preferred-username-and-password)
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LOG](https://workerpool-boxgs.mongodbstitch.com/pages/job.html?collName=queue&jobId=66bb6e638383957117b4b58f)

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Author: kanchana-mongodb

source/includes/steps-configure-prometheus-integration.yaml

@@ -25,6 +25,12 @@ stepnum: 3
 level: 4
 ref: credentials-prometheus
 content: |
+  Prometheus authentication credentials are specifically designed for
+  use with the Prometheus integration in |mms|. |mms| uses these
+  credentials to only access the Prometheus discovery endpoint and
+  scrape Prometheus metrics from |mms| nodes. They are strictly limited
+  to these functions and do not have any additional permissions or
+  capabilities beyond accessing and collecting monitoring data. 
 
   .. important::