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

[cisco-dmytro-hissa]

Description

• Added CA_BUNDLE ("ca_bundle") and CA_BUNDLE_VERSION ("1.0") constants to Client.cs.
• Appended ca_bundle/1.0 to the user agent string.
• Appended (ca_pinning=enabled) / (ca_pinning=disabled) to the user agent string, derived from the current runtime state.
• Pinning reports disabled when either DisableCertificatePinning() or DisableSslCertificateValidation() is used, matching actual behavior (no pinning is performed when SSL validation is off).

How Has This Been Tested?

• TestUserAgentCaBundleVersion — verifies ca_bundle/1.0 is present in the user agent.
• TestUserAgentCaPinningEnabledByDefault — verifies (ca_pinning=enabled) appears by default.
• TestUserAgentCaPinningDisabled — verifies (ca_pinning=disabled) after DisableCertificatePinning().
• TestUserAgentCaPinningDisabledWhenSslValidationDisabled — verifies (ca_pinning=disabled) after DisableSslCertificateValidation().

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)