Allow HTTP request body up to 4 MB. The default is 1 MB, which is too small for
face embeddings for photos with more than a couple of hundred faces.
Roughly, each face embedding is 4KB, but encrypting and base-64-ing the
embedding also has a 30% addition (just from one sample I saw), so this should
allow photos with ~700 faces to go through.
Ref:
- https://nginx.org/en/docs/http/ngx_http_core_module.html#client_max_body_size
