How to create a mount configuration file for systemd in NixOS?

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3

I added

    systemd.mounts = [{
      what = "run-docker-";
      where = "run/docker/";
      description = "Mount to disable docker spam";
      mountConfig = { 
        UnknownOption = "foo";
        LogLevelMax = 0;
      };  
    }];

This caused generation of “/etc/systemd/system/run-docker-.mount” with content

[root@vivy:~]# cat /etc/systemd/system/run-docker-.mount
[Unit]
Description=Mount to disable docker spam

[Mount]
LogLevelMax=0
UnknownOption=foo
What=run-docker-
Where=run/docker/

But, what I want is that the final effect must be creating a directory “/etc/systemd/system/run-docker-.mount.d” containing a file ending with “.conf” containing above content.

I see that there are multiple service.d directories

[root@vivy:~]# ls -ld /etc/systemd/system/*.service.d
dr-xr-xr-x 2 root root 4096 Jan  1  1970 /etc/systemd/system/autovt@.service.d
dr-xr-xr-x 2 root root 4096 Jan  1  1970 /etc/systemd/system/container-getty@.service.d
dr-xr-xr-x 2 root root 4096 Jan  1  1970 /etc/systemd/system/dbus.service.d
...

But I couldn’t find what caused the creation of this directory
on reading https://github.com/NixOS/nixpkgs/blob/fa5e153653a1b48e4a21a14b341e2e01835ba8b5/nixos/modules/services/system/dbus.nix
Q1: How is dbus.service.d directory containing an overrides.conf got generated?

Another solution is creating a custom systemd package, adding the mount.d directory with my own .conf file into the package itself. I believe this might be the cleanest way.
Q2: Is this the best way?