aws: Implementation of IAM Roles anywhere support in aws request signing - part 3 (#39521)

Commit Message: aws: Implementation of IAM Roles anywhere support in aws
request signing - part 3
Additional Description:
Part 3 of 3 patches to implement IAM Roles anywhere capability.
Integrates the previously added components with the credential chain and
unhides the IAM Roles Anywhere credential provider definition in the
API.

Also reverts the coverage limit created in
envoyproxy/envoy#39138 back to default coverage
requirements.

Design brief: envoyproxy/envoy#37440
Part 2 of this patch: envoyproxy/envoy#39025

(https://docs.aws.amazon.com/rolesanywhere/latest/userguide/introduction.html)

Risk Level: Low - extension only changes
Testing: Unit
Docs Changes: N/A
Release Notes: N/A
Platform Specific Features:
[Optional Runtime guard:]
[Optional Fixes #Issue]
[Optional Fixes commit #PR or SHA]
[Optional Deprecated:]
[Optional [API
Considerations](https://github.com/envoyproxy/envoy/blob/main/api/review_checklist.md):]

---------

Signed-off-by: Nigel Brittain <[email protected]>

Mirrored from https://github.com/envoyproxy/envoy @ 1ed3da6fe3c72d15008d8abb110573db3b3e5091

Author: update-envoy[bot]

envoy/extensions/common/aws/v3/credential_provider.proto

@@ -41,7 +41,6 @@ message AwsCredentialProvider {
   bool custom_credential_provider_chain = 4;
 
   // The option to use `IAM Roles Anywhere <https://docs.aws.amazon.com/rolesanywhere/latest/userguide/introduction.html>`_.
-  // [#not-implemented-hide:]
   IAMRolesAnywhereCredentialProvider iam_roles_anywhere_credential_provider = 5;
 
   // The option to use credentials sourced from standard 'AWS configuration files <https://docs.aws.amazon.com/cli/latest/userguide/cli-configure-files.html>'_.
@@ -100,7 +99,6 @@ message CredentialsFileCredentialProvider {
 // Configuration to use `IAM Roles Anywhere <https://docs.aws.amazon.com/rolesanywhere/latest/userguide/introduction.html>`_
 // to retrieve AWS credentials.
 // [#next-free-field: 9]
-// [#not-implemented-hide:]
 message IAMRolesAnywhereCredentialProvider {
   // The ARN of the role to assume via the IAM Roles Anywhere sessions API. See `Configure Roles <https://docs.aws.amazon.com/rolesanywhere/latest/userguide/getting-started.html#getting-started-step2>`_ for more details.
   string role_arn = 1 [(validate.rules).string = {min_len: 1}];