Add CA bundle version and CA pinning status to the user-agent string

[cisco-annikiti]

Description

Append ca_bundle/1.0 and ca_pinning=enabled/ca_pinning=disabled to the User-Agent string based on the current pinning state. The User-Agent header is now set globally on the axios instance rather than per-request on the token endpoint

Motivation and Context

Provides server-side visibility into which CA bundle version clients are running and whether CA pinning is active, enabling monitoring of CA pinning rollout and diagnosing certificate-related connectivity issues

How Has This Been Tested?

• Added unit tests verifying the User-Agent string includes ca_bundle/1.0 and the correct ca_pinning=enabled or ca_pinning=disabled value based on client configuration.
• Existing test suite passes

Types of Changes

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