add apple app attestation data definition

[Ryanmtate]

This pull request introduces support for Apple App Attestation data parsing and validation based on Apple's developer documentation. The main changes include the addition of new data structures and parsing methods for attestation objects, as well as a test to verify certificate chain extraction. The new functionality is grouped into a dedicated module.

Apple App Attestation Support:

• Added the new app_attestation module to src/definitions/mod.rs, which encapsulates all logic related to Apple App Attestation.
• Implemented the AppleAppAttestData and AttestationStatement structs in src/definitions/app_attestation.rs, enabling deserialization and serialization of attestation objects as defined by Apple.
• Provided parsing methods from_base64_string and from_cbor_bytes for AppleAppAttestData, allowing conversion from base64-encoded and CBOR-encoded attestation data respectively.

Testing and Validation:

• Added a test that parses a sample base64-encoded attestation object, extracts the certificate chain, and validates its structure using the X5Chain builder.