Change MD5 hashing to SHA256 for Interactive API examples

[theakshaypant]

Context

• MD5 hashing may allow an attacker to produce collisions on the hash or execute length extension attacks. (CWE-328)
• SHA-2 family hash functions are strong, well-vetted cryptographic hash functions that are currently not known to suffer these weaknesses.
• This PR fixes a weakness identified by Coverity.

Affected examples

Changed hashlib.md5 to hashlib.sha256.

• MXNet Facial Keypoints Detection tutorial
• Dogs vs. Cats tutorial based on vit_pytorch library

[teoparvanov]

Hi @theakshaypant , were you able to successfully run the examples (both before and after the fixes)? If so, please add a "Testing done" section in your PR description.

[rahulga1]

Closing as we wont be fixing any security issues in tutorials and examples folder.