Restore backward-compatible nginx config files for PHP images

[Saipriya-1144]

The official nginx.org package ships minimal config compared to the sury.org nginx package. Customers using custom nginx configs that reference files from the old image would experience hard crashes (nginx: [emerg] ... No such file or directory), causing their sites to go completely down.

Changes

Fix: sites-enabled symlink

• Replaced duplicate COPY default.conf with proper ln -s symlink (sites-enabled → sites-available)

Patch: mime.types and fastcgi_params

• Added missing video/ogg ogv and video/x-matroska mkv to mime.types
• Added missing fastcgi_param REMOTE_USER $remote_user to fastcgi_params

Restore: Missing config files

• fastcgi.conf — used by include fastcgi.conf; (differs from fastcgi_params by including SCRIPT_FILENAME)
• proxy_params — used by include proxy_params; in reverse proxy setups
• snippets/fastcgi-php.conf — standard PHP snippet referenced in many tutorials

Restore: Empty directories

• modules-enabled/ — prevents crash if customer config has include /etc/nginx/modules-enabled/*.conf;

• modules-available/ — existed in old image (was empty)

• The purpose of this PR is explained in this message or in an issue. If an issue please include a reference as #<issue_number>.

• Tests are included and/or updated for code changes.

• Proper license headers are included in each file.

[ShilpiRach]

Looks good!