Disable CA Pinning: Add constructor parameter

[cisco-annikiti]

Description

Add enableCAPinning constructor parameter to the Duo API client that allows disabling CA pinning. When disabled, the TLS library validates connections using Node.js's default CA bundle instead of the pinned certificates. TLS verification remains enforced in all cases.

Motivation and Context

Part of the CA Pinning Standardization initiative. Provides a configuration option to disable CA pinning for scenarios where customers cannot upgrade and need an immediate workaround during certificate changes.

How Has This Been Tested?

Added 3 unit tests covering:

• CA pinning is enabled by default
• CA pinning can be disabled via constructor parameter (no ca option on request)
• TLS verification is still enforced when pinning is disabled
  All tests pass (npm test).

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)