fix!: remove the ArgoCD namespace variable

Since we are hardcoding the namespace variable on all modules, the variable to set the ArgoCD namespace will no longer be needed as well.

main.tf

@@ -7,10 +7,7 @@ resource "argocd_project" "this" {
 
   metadata {
     name      = var.destination_cluster != "in-cluster" ? "longhorn-${var.destination_cluster}" : "longhorn"
-    namespace = var.argocd_namespace
-    annotations = {
-      "devops-stack.io/argocd_namespace" = var.argocd_namespace
-    }
+    namespace = "argocd"
   }
 
   spec {
@@ -40,7 +37,7 @@ data "utils_deep_merge_yaml" "values" {
 resource "argocd_application" "this" {
   metadata {
     name      = var.destination_cluster != "in-cluster" ? "longhorn-${var.destination_cluster}" : "longhorn"
-    namespace = var.argocd_namespace
+    namespace = "argocd"
     labels = merge({
       "application" = "longhorn"
       "cluster"     = var.destination_cluster

variables.tf

@@ -20,12 +20,6 @@ variable "cluster_issuer" {
   default     = "selfsigned-issuer"
 }
 
-variable "argocd_namespace" {
-  description = "Namespace used by Argo CD where the Application and AppProject resources should be created."
-  type        = string
-  default     = "argocd"
-}
-
 variable "argocd_project" {
   description = "Name of the Argo CD AppProject where the Application should be created. If not set, the Application will be created in a new AppProject only for this Application."
   type        = string