fix(agent/agentcontainers): read WorkspaceFolder from config (#18467)

Instead of exec'ing `pwd` inside of the container, we instead read
`WorkspaceFolder` from the outcome of `read-configuration`.

agent/agentcontainers/devcontainercli.go

@@ -22,6 +22,7 @@ import (
 type DevcontainerConfig struct {
 	MergedConfiguration DevcontainerMergedConfiguration `json:"mergedConfiguration"`
 	Configuration       DevcontainerConfiguration       `json:"configuration"`
+	Workspace           DevcontainerWorkspace           `json:"workspace"`
 }
 
 type DevcontainerMergedConfiguration struct {
@@ -46,6 +47,10 @@ type CoderCustomization struct {
 	Name        string                       `json:"name,omitempty"`
 }
 
+type DevcontainerWorkspace struct {
+	WorkspaceFolder string `json:"workspaceFolder"`
+}
+
 // DevcontainerCLI is an interface for the devcontainer CLI.
 type DevcontainerCLI interface {
 	Up(ctx context.Context, workspaceFolder, configPath string, opts ...DevcontainerCLIUpOptions) (id string, err error)