feat: allow for different docker socket path in docker-based templates (#15035) (#15049)

This PR fixes #15035, I have tested it on my instance and it works as
expected.

examples/templates/devcontainer-docker/main.tf

@@ -13,9 +13,19 @@ terraform {
   }
 }
 
+variable "docker_socket" {
+  default     = ""
+  description = "(Optional) Docker socket URI"
+  type        = string
+}
+
 provider "coder" {}
-provider "docker" {}
+provider "docker" {
+  # Defaulting to null if the variable is an empty string lets us have an optional variable without having to set our own default
+  host = var.docker_socket != "" ? var.docker_socket : null
+}
 provider "envbuilder" {}
+
 data "coder_provisioner" "me" {}
 data "coder_workspace" "me" {}
 data "coder_workspace_owner" "me" {}

examples/templates/docker/main.tf

@@ -13,14 +13,19 @@ locals {
   username = data.coder_workspace_owner.me.name
 }
 
-data "coder_provisioner" "me" {
+variable "docker_socket" {
+  default     = ""
+  description = "(Optional) Docker socket URI"
+  type        = string
 }
 
 provider "docker" {
+  # Defaulting to null if the variable is an empty string lets us have an optional variable without having to set our own default
+  host = var.docker_socket != "" ? var.docker_socket : null
 }
 
-data "coder_workspace" "me" {
-}
+data "coder_provisioner" "me" {}
+data "coder_workspace" "me" {}
 data "coder_workspace_owner" "me" {}
 
 resource "coder_agent" "main" {