Allow serving static files on Google App Engine second generation PHP flex runtime

nginx-app.conf

# This file is used by App Engine flex environment PHP runtime by name convention nginx-app.conf:
# https://cloud.google.com/appengine/docs/flexible/php/runtime#customize_nginx

# App Engine rewrites everything to index.php$uri, this prevents us to catch
# anything else with `location` block, so the hack is to catch it with another
# rewrite that lets us handle in our own `location ~ ^/myapp` below
# (https://github.com/GoogleCloudPlatform/buildpacks/blob/ff2ea2737a928087dcec192bf3ce103dc356ad5e/pkg/nginx/nginx.go#L93)
rewrite ^/index.php(.*)$ /myapp$1;

# Handle this our way first because we want to try serving a file if it matches,
# otherwise go back to app engine's default index.php `location` block.
location ~ ^/myapp(.*)$ {
    # We can't send to /index.php$1 directly here because that would be caught
    # by our `rewrite ^/index.php` causing infinite rewrites. So instead send
    # this to the @fallback `location` below where we can do a final rewrite
    # with the `last` keyword.
    try_files $1 @fallback;
}
location @fallback {
    rewrite ^/myapp(.*)$ /index.php$1 last;
}