Docs: help users connect to Prometheus using SigV4 (#30232)

* Add sigv4 overview and links to AWS docs

* minor wording tweak

* Update prometheus.md

* move supported version in Prometheus-AMP docs

Co-authored-by: Diana Payton <52059945+oddlittlebird@users.noreply.github.com>

* move supported version

Co-authored-by: Diana Payton <52059945+oddlittlebird@users.noreply.github.com>

* move version support note

Co-authored-by: Diana Payton <52059945+oddlittlebird@users.noreply.github.com>

docs/sources/datasources/prometheus.md

@@ -170,3 +170,13 @@ datasources:
     access: proxy
     url: http://localhost:9090
 ```
+
+## Amazon Managed Service for Prometheus
+
+The Prometheus data source works with Amazon Managed Service for Prometheus. If you are using an AWS Identity and Access Management (IAM) policy to control access to your Amazon Managed Service for Prometheus domain, then you must use AWS Signature Version 4 (AWS SigV4) to sign  all requests to that domain. For more details on AWS SigV4, refer to the [AWS documentation](https://docs.aws.amazon.com/general/latest/gr/signature-version-4.html).
+
+> **Note:** Grafana version 7.3.5 or higher is required to use SigV4 authentication.
+
+To connect the Prometheus data source to Amazon Managed Service for Prometheus using SigV4 authentication, refer to the AWS guide to [Set up Grafana open source or Grafana Enterprise for use with AMP](https://docs.aws.amazon.com/prometheus/latest/userguide/AMP-onboard-query-standalone-grafana.html). 
+
+If you are running Grafana in an Amazon EKS cluster, follow the AWS guide to [Query using Grafana running in an Amazon EKS cluster](https://docs.aws.amazon.com/prometheus/latest/userguide/AMP-onboard-query-grafana-7.3.html).