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/agentcontainers/devcontainer.go

@@ -0,0 +1,98 @@
+package agentcontainers
+
+import (
+	"context"
+	"fmt"
+	"os"
+	"path/filepath"
+	"strings"
+
+	"cdr.dev/slog"
+
+	"github.com/coder/coder/v2/codersdk"
+)
+
+const devcontainerUpScriptTemplate = `
+if ! which devcontainer > /dev/null 2>&1; then
+  echo "ERROR: Unable to start devcontainer, @devcontainers/cli is not installed."
+  exit 1
+fi
+devcontainer up %s
+`
+
+// ExtractAndInitializeDevcontainerScripts extracts devcontainer scripts from
+// the given scripts and devcontainers. The devcontainer scripts are removed
+// from the returned scripts so that they can be run separately.
+//
+// Dev Containers have an inherent dependency on start scripts, since they
+// initialize the workspace (e.g. git clone, npm install, etc). This is
+// important if e.g. a Coder module to install @devcontainer/cli is used.
+func ExtractAndInitializeDevcontainerScripts(
+	logger slog.Logger,
+	expandPath func(string) (string, error),
+	devcontainers []codersdk.WorkspaceAgentDevcontainer,
+	scripts []codersdk.WorkspaceAgentScript,
+) (filteredScripts []codersdk.WorkspaceAgentScript, devcontainerScripts []codersdk.WorkspaceAgentScript) {
+ScriptLoop:
+	for _, script := range scripts {
+		for _, dc := range devcontainers {
+			// The devcontainer scripts match the devcontainer ID for
+			// identification.
+			if script.ID == dc.ID {
+				dc = expandDevcontainerPaths(logger, expandPath, dc)
+				devcontainerScripts = append(devcontainerScripts, devcontainerStartupScript(dc, script))
+				continue ScriptLoop
+			}
+		}
+
+		filteredScripts = append(filteredScripts, script)
+	}
+
+	return filteredScripts, devcontainerScripts
+}
+
+func devcontainerStartupScript(dc codersdk.WorkspaceAgentDevcontainer, script codersdk.WorkspaceAgentScript) codersdk.WorkspaceAgentScript {
+	var args []string
+	args = append(args, fmt.Sprintf("--workspace-folder %q", dc.WorkspaceFolder))
+	if dc.ConfigPath != "" {
+		args = append(args, fmt.Sprintf("--config %q", dc.ConfigPath))
+	}
+	cmd := fmt.Sprintf(devcontainerUpScriptTemplate, strings.Join(args, " "))
+	script.Script = cmd
+	// Disable RunOnStart, scripts have this set so that when devcontainers
+	// have not been enabled, a warning will be surfaced in the agent logs.
+	script.RunOnStart = false
+	return script
+}
+
+func expandDevcontainerPaths(logger slog.Logger, expandPath func(string) (string, error), dc codersdk.WorkspaceAgentDevcontainer) codersdk.WorkspaceAgentDevcontainer {
+	logger = logger.With(slog.F("devcontainer", dc.Name), slog.F("workspace_folder", dc.WorkspaceFolder), slog.F("config_path", dc.ConfigPath))
+
+	if wf, err := expandPath(dc.WorkspaceFolder); err != nil {
+		logger.Warn(context.Background(), "expand devcontainer workspace folder failed", slog.Error(err))
+	} else {
+		dc.WorkspaceFolder = wf
+	}
+	if dc.ConfigPath != "" {
+		// Let expandPath handle home directory, otherwise assume relative to
+		// workspace folder or absolute.
+		if dc.ConfigPath[0] == '~' {
+			if cp, err := expandPath(dc.ConfigPath); err != nil {
+				logger.Warn(context.Background(), "expand devcontainer config path failed", slog.Error(err))
+			} else {
+				dc.ConfigPath = cp
+			}
+		} else {
+			dc.ConfigPath = relativePathToAbs(dc.WorkspaceFolder, dc.ConfigPath)
+		}
+	}
+	return dc
+}
+
+func relativePathToAbs(workdir, path string) string {
+	path = os.ExpandEnv(path)
+	if !filepath.IsAbs(path) {
+		path = filepath.Join(workdir, path)
+	}
+	return path
+}