Docker: increase maximum file upload size to 10 MiB

Docker: increase maximum file upload size to 10 MiB

Relates to https://github.com/shaarli/Shaarli/issues/681

Changed:
- nginx+php-fpm: set maximum upload size to 10 MiB

See:
- https://nginx.org/en/docs/http/ngx_http_core_module.html#client_max_body_size
- https://secure.php.net/manual/en/ini.core.php#ini.post-max-size
- https://secure.php.net/manual/en/ini.core.php#ini.upload-max-filesize

Signed-off-by: VirtualTam <virtualtam@flibidi.net>