GODRIVER-3175 Add Kubernetes support for OIDC.

[matthewdale]

GODRIVER-3175

Summary

• Support the "k8s" OIDC environment for AKS, EKS, and GKE.
• Update connection string validation for new OIDC connection string tests.
• Add tests for the "k8s" OIDC environment.
• Use the same Evergreen task group configuration for all OIDC task groups.
• Remove unnecessary batchtime config for other OIDC test tasks.
• Remove accidental duplication of OIDC options subtest in TestClientOptions.

Background & Motivation

From DRIVERS-2882:

Drivers will add a "k8s" implementation of an OIDC_CALLBACK that handles AWS EKS, GCP GKE, and Azure AKS.

[mongodb-drivers-pr-bot]

API Change Report

./v2/x/mongo/driver/auth

compatible changes

K8SEnvironmentValue: added

PR Overview

This pull request adds Kubernetes support for OIDC authentication by extending both the test suite and driver configuration. Key changes include:

• Adding a new “k8s” test case (machinek8s) and corresponding callback (k8sOIDCCallback) for Kubernetes in the OIDC test harness.
• Standardizing error message formatting and OIDC validation logic in client options and driver authentication.
• Updating Evergreen configuration and test cases to include Kubernetes OIDC tests.

Reviewed Changes

File	Description
internal/cmd/testoidcauth/main.go	Introduces the "k8s" case and adds the machinek8s test to validate Kubernetes OIDC.
mongo/options/clientoptions.go	Updates error messages and validation checks for OIDC properties.
x/mongo/driver/auth/oidc.go	Adds constants and a new k8sOIDCCallback for Kubernetes token file handling.
.evergreen/config.yml	Modifies test task definitions to run new Kubernetes OIDC tests.
x/mongo/driver/auth/auth_spec_test.go	Revises test grouping and skipped tests to reflect updated test scenarios.
mongo/options/clientoptions_test.go	Adjusts test expectations for error message formatting in OIDC configuration tests.

Copilot reviewed 10 out of 10 changed files in this pull request and generated no comments.