DOC-315: Cross-link service-specific IAM condition keys

Add a "Service-Specific Condition Keys" section to the IAM Coverage
page linking out to the EC2 and RAM service docs, and link the
existing global condition keys to AWS's reference page. Addresses
review feedback from Viren on PR #812.

Author: quetzalliwrites

src/content/docs/aws/developer-tools/security-testing/iam-coverage.md

@@ -152,7 +152,7 @@ It only includes operations performed with a principal, not as root, so test set
 |                | - StringEqualsIgnoreCase                                                             |
 |                | - StringLike                                                                         |
 |                | - ArnLike/ArnEquals                                                                  |
-|                | Supported condition keys:                                                            |
+|                | Supported [global condition keys](https://docs.aws.amazon.com/IAM/latest/UserGuide/reference_policies_condition-keys.html): |
 |                | - aws:RequestedRegion                                                                |
 |                | - aws:PrincipalArn                                                                   |
 |                | - aws:SourceArn                                                                      |
@@ -161,6 +161,12 @@ It only includes operations performed with a principal, not as root, so test set
 |                | - aws:RequestTag                                                                     |
 |                | - aws:PrincipalTag                                                                    |
 
+## Service-Specific Condition Keys
+
+In addition to the global condition keys above, some services support their own condition keys, matching AWS's [per-service condition key reference](https://docs.aws.amazon.com/service-authorization/latest/reference/reference_policies_actions-resources-contextkeys.html):
+
+- [EC2](/aws/services/ec2/#iam-condition-keys): `ec2:MetadataHttpTokens`, `ec2:Attribute/<AttributeName>`
+- [RAM](/aws/services/ram/#iam-condition-keys): `ram:RequestedAllowsExternalPrincipals`
 
 ## Current Limitations