Add documentation for the AWS_EC2_METADATA_DISABLED environment varia…

…ble.

Fixes aws/aws-cli#5623.

doc_source/cli-configure-envvars.md

@@ -81,6 +81,10 @@ If defined, this environment variable overrides the value for the profile settin
 Specifies the AWS Region to send the request to\.  
 If defined, this environment variable overrides the value for the profile setting `region`\. You can override this environment variable by using the `--region` command line parameter\.
 
+[`AWS_EC2_METADATA_DISABLED`](cli-configure-metadata.md)  
+Disables the use of the AWS EC2 instance metadata service (IMDS)\.  
+If set to false, user credentials or configuration (like the region) will not be requested from IMDS\.
+
 [`AWS_MAX_ATTEMPTS`](cli-configure-files.md#cli-config-max_attempts)  
 Specifies a value of maximum retry attempts the AWS CLI retry handler uses, where the initial call counts toward the value that you provide\. For more information on retries, see [AWS CLI retries](cli-configure-retries.md)\.  
 If defined, this environment variable overrides the value for the profiles setting `max_attempts`\.
@@ -120,4 +124,4 @@ Specifies how the AWS CLI determines the AWS service endpoint that the AWS CLI c
 + The default value for AWS CLI version 2 is `regional`\.
 You can specify one of two values:  
 + **`legacy`** – Uses the global STS endpoint, `sts.amazonaws.com`, for the following AWS Regions: `ap-northeast-1`, `ap-south-1`, `ap-southeast-1`, `ap-southeast-2`, `aws-global`, `ca-central-1`, `eu-central-1`, `eu-north-1`, `eu-west-1`, `eu-west-2`, `eu-west-3`, `sa-east-1`, `us-east-1`, `us-east-2`, `us-west-1`, and `us-west-2`\. All other Regions automatically use their respective regional endpoint\.
-+ **`regional`** – The AWS CLI always uses the AWS STS endpoint for the currently configured Region\. For example, if the client is configured to use `us-west-2`, all calls to AWS STS are made to the regional endpoint `sts.us-west-2.amazonaws.com` instead of the global `sts.amazonaws.com` endpoint\. To send a request to the global endpoint while this setting is enabled, you can set the Region to `aws-global`\.
++ **`regional`** – The AWS CLI always uses the AWS STS endpoint for the currently configured Region\. For example, if the client is configured to use `us-west-2`, all calls to AWS STS are made to the regional endpoint `sts.us-west-2.amazonaws.com` instead of the global `sts.amazonaws.com` endpoint\. To send a request to the global endpoint while this setting is enabled, you can set the Region to `aws-global`\.