nixos/nextcloud: fix nginx-config for Nextcloud 19 and older

It seems as I misconfigured `nginx` for certain cases such as the
`ldap`-plugin[1] in 42f6244. This patch
fixes the `nginx`-config to match the upstream recommendations[2].

Also added a comment to the module to remind myself to ensure that
`nginx` will work with both v19 and v20 as soon as the latter is
released and can be packaged in `nixpkgs`.

Co-authored-by: nivadis <nivadis@users.noreply.github.com>

[1] nextcloud/server#16194 (comment)
[2] https://docs.nextcloud.com/server/19/admin_manual/installation/nginx.html

(cherry picked from commit 8d8871c)

nixos/modules/services/web-apps/nextcloud.nix

@@ -528,7 +528,7 @@ in {
               };
               "/" = {
                 priority = 900;
-                extraConfig = "try_files $uri $uri/ /index.php$request_uri;";
+                extraConfig = "rewrite ^ /index.php;";
               };
               "~ ^/store-apps" = {
                 priority = 201;
@@ -552,7 +552,7 @@ in {
               "~ ^/(?:\\.|autotest|occ|issue|indie|db_|console)".extraConfig = ''
                 return 404;
               '';
-              "~ \\.php(?:$|/)" = {
+              "~ ^\\/(?:index|remote|public|cron|core\\/ajax\\/update|status|ocs\\/v[12]|updater\\/.+|oc[ms]-provider\\/.+|.+\\/richdocumentscode\\/proxy)\\.php(?:$|\\/)" = {
                 priority = 500;
                 extraConfig = ''
                   include ${config.services.nginx.package}/conf/fastcgi.conf;