[C2] File upload MIME validation

[ywarnier]

Restore the whitelist/blacklist validation available in C1 on all upload endpoints (n°8)

[christianbeeznest]

It is checked with this commit f12dfd3

Implemented a global upload filename/extension policy (C1-like whitelist/blacklist + .php/.htaccess neutralization) applied automatically on every request with multipart uploads via a kernel.request subscriber. Also hardened ZIP “uncompress” imports by filtering/sanitizing each entry (blocks path traversal, skips junk, applies the same policy) instead of blindly extracting everything.

[ywarnier]

The error message will be improved in the future, but essentially that works for me. I put testing26 on whitelist mode and tried to upload an ".exe" file and it prevented it (with a message mentioning a possible network or firewall error - I guess this message comes from the uploader library).