Config clash when enabling Blitz API and the Raspiblitz WebUI with default values

Both services are bound to the path `/` by default.

```
~> sudo nixblitz apply
doas (admin@nixblitzvm) password:
warning: Git tree '/mnt/data/config' is dirty
warning: Nix search path entry '/nix/var/nix/profiles/per-user/root/channels' does not exist, ignoring
building the system configuration...
warning: Git tree '/mnt/data/config' is dirty
warning: Nix search path entry '/nix/var/nix/profiles/per-user/root/channels' does not exist, ignoring
error:
… while calling the 'head' builtin
at /nix/store/1zw47fx5h4x65n914j4b9iz0j3v17aw0-source/lib/attrsets.nix:1534:13:
1533| if length values == 1 || pred here (elemAt values 1) (head values) then
1534| head values
| ^
1535| else
… while evaluating the attribute 'value'
at /nix/store/1zw47fx5h4x65n914j4b9iz0j3v17aw0-source/lib/modules.nix:1084:7:
1083| // {
1084| value = addErrorContext "while evaluating the option `${showOption loc}':" value;
| ^
1085| inherit (res.defsFinal') highestPrio;
… while evaluating the option `system.build.toplevel':
… while evaluating definitions from `/nix/store/1zw47fx5h4x65n914j4b9iz0j3v17aw0-source/nixos/modules/system/activation/top-level.nix':
… while evaluating the option `services.nginx.virtualHosts.localhost.locations."/".proxyPass':
(stack trace truncated; use '--show-trace' to show the full, detailed trace)
error: The option `services.nginx.virtualHosts.localhost.locations."/".proxyPass' has conflicting definition values:
- In `/nix/store/aj5l32h6s2c0fqlq9i8d67i3p2al8ixd-source/modules/nixblitz-webapp.nix': "http://127.0.0.1:8181/"
- In `/nix/store/jr6h6vyh60yxg2kh462fkrym5l3ij0y5-source/modules/blitz_api.nix': "http://127.0.0.1:2121/"
Use `lib.mkForce value` or `lib.mkDefault value` to change the priority on any of these definitions.
--- Process finished with status: exit status: 1 ---
Error applying changes: Unknown error
├╴at cli/src/commands/apply.rs:12:10
│
╰─▶ Unable to apply changes
├╴at /build/packages/nixblitzlib/src/utils.rs:254:33
╰╴Command exited with non-zero status.
```