feat(agent): add devcontainer autostart support (#17076)

This change adds support for devcontainer autostart in workspaces. The
preconditions for utilizing this feature are:

1. The `coder_devcontainer` resource must be defined in Terraform
2. By the time the startup scripts have completed,
	- The `@devcontainers/cli` tool must be installed
	- The given workspace folder must contain a devcontainer configuration

Example Terraform:

```tf
resource "coder_devcontainer" "coder" {
  agent_id         = coder_agent.main.id
  workspace_folder = "/home/coder/coder"
  config_path      = ".devcontainer/devcontainer.json" # (optional)
}
```

Closes #16423

agent/agentscripts/agentscripts.go

@@ -80,6 +80,21 @@ func New(opts Options) *Runner {
 
 type ScriptCompletedFunc func(context.Context, *proto.WorkspaceAgentScriptCompletedRequest) (*proto.WorkspaceAgentScriptCompletedResponse, error)
 
+type runnerScript struct {
+	runOnPostStart bool
+	codersdk.WorkspaceAgentScript
+}
+
+func toRunnerScript(scripts ...codersdk.WorkspaceAgentScript) []runnerScript {
+	var rs []runnerScript
+	for _, s := range scripts {
+		rs = append(rs, runnerScript{
+			WorkspaceAgentScript: s,
+		})
+	}
+	return rs
+}
+
 type Runner struct {
 	Options
 
@@ -90,7 +105,7 @@ type Runner struct {
 	closeMutex      sync.Mutex
 	cron            *cron.Cron
 	initialized     atomic.Bool
-	scripts         []codersdk.WorkspaceAgentScript
+	scripts         []runnerScript
 	dataDir         string
 	scriptCompleted ScriptCompletedFunc
 
@@ -119,16 +134,35 @@ func (r *Runner) RegisterMetrics(reg prometheus.Registerer) {
 	reg.MustRegister(r.scriptsExecuted)
 }
 
+// InitOption describes an option for the runner initialization.
+type InitOption func(*Runner)
+
+// WithPostStartScripts adds scripts that should be run after the workspace
+// start scripts but before the workspace is marked as started.
+func WithPostStartScripts(scripts ...codersdk.WorkspaceAgentScript) InitOption {
+	return func(r *Runner) {
+		for _, s := range scripts {
+			r.scripts = append(r.scripts, runnerScript{
+				runOnPostStart:       true,
+				WorkspaceAgentScript: s,
+			})
+		}
+	}
+}
+
 // Init initializes the runner with the provided scripts.
 // It also schedules any scripts that have a schedule.
 // This function must be called before Execute.
-func (r *Runner) Init(scripts []codersdk.WorkspaceAgentScript, scriptCompleted ScriptCompletedFunc) error {
+func (r *Runner) Init(scripts []codersdk.WorkspaceAgentScript, scriptCompleted ScriptCompletedFunc, opts ...InitOption) error {
 	if r.initialized.Load() {
 		return xerrors.New("init: already initialized")
 	}
 	r.initialized.Store(true)
-	r.scripts = scripts
+	r.scripts = toRunnerScript(scripts...)
 	r.scriptCompleted = scriptCompleted
+	for _, opt := range opts {
+		opt(r)
+	}
 	r.Logger.Info(r.cronCtx, "initializing agent scripts", slog.F("script_count", len(scripts)), slog.F("log_dir", r.LogDir))
 
 	err := r.Filesystem.MkdirAll(r.ScriptBinDir(), 0o700)
@@ -136,13 +170,13 @@ func (r *Runner) Init(scripts []codersdk.WorkspaceAgentScript, scriptCompleted S
 		return xerrors.Errorf("create script bin dir: %w", err)
 	}
 
-	for _, script := range scripts {
+	for _, script := range r.scripts {
 		if script.Cron == "" {
 			continue
 		}
 		script := script
 		_, err := r.cron.AddFunc(script.Cron, func() {
-			err := r.trackRun(r.cronCtx, script, ExecuteCronScripts)
+			err := r.trackRun(r.cronCtx, script.WorkspaceAgentScript, ExecuteCronScripts)
 			if err != nil {
 				r.Logger.Warn(context.Background(), "run agent script on schedule", slog.Error(err))
 			}
@@ -186,6 +220,7 @@ type ExecuteOption int
 const (
 	ExecuteAllScripts ExecuteOption = iota
 	ExecuteStartScripts
+	ExecutePostStartScripts
 	ExecuteStopScripts
 	ExecuteCronScripts
 )
@@ -196,6 +231,7 @@ func (r *Runner) Execute(ctx context.Context, option ExecuteOption) error {
 	for _, script := range r.scripts {
 		runScript := (option == ExecuteStartScripts && script.RunOnStart) ||
 			(option == ExecuteStopScripts && script.RunOnStop) ||
+			(option == ExecutePostStartScripts && script.runOnPostStart) ||
 			(option == ExecuteCronScripts && script.Cron != "") ||
 			option == ExecuteAllScripts
 
@@ -205,7 +241,7 @@ func (r *Runner) Execute(ctx context.Context, option ExecuteOption) error {
 
 		script := script
 		eg.Go(func() error {
-			err := r.trackRun(ctx, script, option)
+			err := r.trackRun(ctx, script.WorkspaceAgentScript, option)
 			if err != nil {
 				return xerrors.Errorf("run agent script %q: %w", script.LogSourceID, err)
 			}