fix(kasmvnc): update kasmvnc desktop environment list to match upstream (#598)

## Description

This PR makes the following changes to `coder/modules/kasmvnc`:

- Update desktop environment list for the KasmVNC module

Currently upstream supports a number of [additional Desktop
Environments](https://github.com/kasmtech/KasmVNC/blob/v1.4.0/unix/vncserver.man#L56-L67).
The change updates the list so that DEs like Mate are supported. Do note
that `manual` is also supported if `$HOME/.vnc/xstartup` is supplied, so
this has been added as another option, too.

## Type of Change

- [ ] New module
- [ ] New template
- [X] Bug fix
- [ ] Feature/enhancement
- [ ] Documentation
- [ ] Other

## Module Information

<!-- Delete this section if not applicable -->

**Path:** `registry/coder/modules/kasmvnc`
**New version:** `v1.2.7`  
**Breaking change:** [ ] Yes [X] No

## Testing & Validation

- [X] Tests pass (`bun test`)
- [X] Code formatted (`bun fmt`)
- [X] Changes tested locally

## Related Issues

None

Co-authored-by: DevCats <christofer@coder.com>

registry/coder/modules/kasmvnc/README.md

@@ -14,7 +14,7 @@ Automatically install [KasmVNC](https://kasmweb.com/kasmvnc) in a workspace, and
 module "kasmvnc" {
   count               = data.coder_workspace.me.start_count
   source              = "registry.coder.com/coder/kasmvnc/coder"
-  version             = "1.2.6"
+  version             = "1.2.7"
   agent_id            = coder_agent.example.id
   desktop_environment = "xfce"
   subdomain           = true

registry/coder/modules/kasmvnc/main.tf

@@ -31,7 +31,7 @@ variable "desktop_environment" {
   description = "Specifies the desktop environment of the workspace. This should be pre-installed on the workspace."
 
   validation {
-    condition     = contains(["xfce", "kde", "gnome", "lxde", "lxqt"], var.desktop_environment)
+    condition     = contains(["cinnamon", "mate", "lxde", "lxqt", "kde", "gnome", "xfce", "manual"], var.desktop_environment)
     error_message = "Invalid desktop environment. Please specify a valid desktop environment."
   }
 }