Output prometheus-remote: documents SigV4 configurations

Author: olegbespalov

docs/sources/k6/next/results-output/real-time/prometheus-remote-write.md

@@ -168,6 +168,9 @@ k6 has special options for remote write output.
 | `K6_PROMETHEUS_RW_CLIENT_CERTIFICATE` | `string` | A path to the PEM (Privacy-Enhanced Mail) formatted client certificate. |
 | `K6_PROMETHEUS_RW_CLIENT_CERTIFICATE_KEY` | `string` | A path to the PEM formatted client private key. |
 | `K6_PROMETHEUS_RW_BEARER_TOKEN` | `string` | Sets the Authorization Bearer Token Header. |
+| `K6_PROMETHEUS_RW_SIGV4_REGION` | `string` | Sets the AWS region where the workspace is. Along with the others `K6_PROMETHEUS_RW_SIGV4_*` configurations enables signing requests. |
+| `K6_PROMETHEUS_RW_SIGV4_ACCESS_KEY` | `string` | Sets the AWS access key. |
+| `K6_PROMETHEUS_RW_SIGV4_SECRET_KEY` | `string` | Sets the AWS secret key. |
 
 ### Stale trend metrics