fix(agent/agentcontainers): treat customizations as array (#18357)

This PR fixes a mistake from the previous PR
https://github.com/coder/coder/pull/18342. Merged configuration results
in the customization being an array not an object.

This PR also moves `displayApps` from being an array to being an object,
like the terraform provider has.

agent/agentcontainers/devcontainercli.go

@@ -27,11 +27,11 @@ type DevcontainerConfiguration struct {
 }
 
 type DevcontainerCustomizations struct {
-	Coder *CoderCustomization `json:"coder,omitempty"`
+	Coder []CoderCustomization `json:"coder,omitempty"`
 }
 
 type CoderCustomization struct {
-	DisplayApps []codersdk.DisplayApp `json:"displayApps,omitempty"`
+	DisplayApps map[codersdk.DisplayApp]bool `json:"displayApps,omitempty"`
 }
 
 // DevcontainerCLI is an interface for the devcontainer CLI.