fix(coder/modules/goose): update default values for Goose provider and model variables to empty strings (#106)

- Changed default values from null to empty strings for
`experiment_goose_provider` and `experiment_goose_model` variables in
main.tf to ensure compatibility and avoid null interpolation issues.

registry/coder/modules/goose/README.md

@@ -14,7 +14,7 @@ Run the [Goose](https://block.github.io/goose/) agent in your workspace to gener
 ```tf
 module "goose" {
   source        = "registry.coder.com/coder/goose/coder"
-  version       = "1.1.0"
+  version       = "1.1.1"
   agent_id      = coder_agent.example.id
   folder        = "/home/coder"
   install_goose = true
@@ -90,7 +90,7 @@ resource "coder_agent" "main" {
 module "goose" {
   count         = data.coder_workspace.me.start_count
   source        = "registry.coder.com/coder/goose/coder"
-  version       = "1.1.0"
+  version       = "1.1.1"
   agent_id      = coder_agent.example.id
   folder        = "/home/coder"
   install_goose = true
@@ -148,7 +148,7 @@ Run Goose as a standalone app in your workspace. This will install Goose and run
 ```tf
 module "goose" {
   source        = "registry.coder.com/coder/goose/coder"
-  version       = "1.1.0"
+  version       = "1.1.1"
   agent_id      = coder_agent.example.id
   folder        = "/home/coder"
   install_goose = true

registry/coder/modules/goose/main.tf

@@ -69,13 +69,13 @@ variable "experiment_auto_configure" {
 variable "experiment_goose_provider" {
   type        = string
   description = "The provider to use for Goose (e.g., anthropic)."
-  default     = null
+  default     = ""
 }
 
 variable "experiment_goose_model" {
   type        = string
   description = "The model to use for Goose (e.g., claude-3-5-sonnet-latest)."
-  default     = null
+  default     = ""
 }
 
 variable "experiment_pre_install_script" {