Add EKSProvider for AWS credentials using Pod Identity agent and integrate into AWSCredentialProvider chain

[vipulsharma2190]

Summary

This pull request introduces a new EKSProvider to the AWS credential provider chain in the MongoDB Go driver. The EKSProvider enables the driver to retrieve AWS credentials from the endpoint specified by the AWS_CONTAINER_CREDENTIALS_FULL_URI environment variable.

Background & Motivation

AWS recently introduced the Pod Identity agent for EKS, which provides IAM credentials to pods via a local HTTP endpoint. The agent sets the AWS_CONTAINER_CREDENTIALS_FULL_URI environment variable in the pod, typically pointing to a URL like http://169.254.170.23/v1/credentials.

The implementation of EKSProvider is essentially similar to the existing ECSProvider, with the main difference being the use of a different environment variable and endpoint for credential retrieval. This change ensures the driver can authenticate seamlessly in EKS environments using Pod Identity.

AWS SDK: Container Credentials
Pod Identity Agent

[prestonvasquez]

DRIVERS-2945 (Support for AWS EKS Pod Identity) is currently blocked, noting:

Drivers that optionally support an AWS SDK will not be expected to implement support in the non-SDK version of the logic

Go Driver plans to optionally support aws-sdk-go-v2 with GODRIVER-3567.

CC: @matthewdale

[prestonvasquez]

@fdgod09 See this comment for closure reason: #2146 (comment)

As a stopgap, users can register their own authenticator using auth.RegisterAuthenticatorFactory:

V1: https://gist.github.com/prestonvasquez/4c339bf9e26217c65172b9849a43d505
V2: https://gist.github.com/prestonvasquez/d36d3c6bf57a574b5451ee53277236f1