Add support for OIDC auth to the publisher CLI

[elnaterator]

Motivation and Context

Issue #604

Adds support for OIDC authentication via the publisher CLI. This enables users to publish internal MCP servers to subregistries that are configured with OIDC auth, such as enterprise registries, using the same mcp-publisher CLI.

How Has This Been Tested?

Manually tested locally using Okta and Auth0 as OIDC identity providers.

Breaking Changes

None

Types of changes

• [ ] Bug fix (non-breaking change which fixes an issue)
• [x] New feature (non-breaking change which adds functionality)
• [ ] Breaking change (fix or feature that would cause existing functionality to change)
• [ ] Documentation update

Checklist

• [x] I have read the MCP Documentation
• [x] My code follows the repository's style guidelines
• [x] New and existing tests pass locally
• [x] I have added appropriate error handling
• [x] I have added or updated documentation as needed