cli: add Terraform log support (#1620)

* add Terraform logging

* add TF logging to CLI

* fix path

* only create file if logging is enabled

* update bazel files

* register persistent flags manually

* clidocgen

* move logging code to separate file

* reword yes flag parsing error

* update bazel buildfile

* factor out log level setting

cli/internal/terraform/logging.go

@@ -0,0 +1,75 @@
+/*
+Copyright (c) Edgeless Systems GmbH
+
+SPDX-License-Identifier: AGPL-3.0-only
+*/
+
+package terraform
+
+import (
+	"fmt"
+	"strings"
+)
+
+const (
+	// LogLevelNone represents a log level that does not produce any output.
+	LogLevelNone LogLevel = iota
+	// LogLevelError enables log output at ERROR level.
+	LogLevelError
+	// LogLevelWarn enables log output at WARN level.
+	LogLevelWarn
+	// LogLevelInfo enables log output at INFO level.
+	LogLevelInfo
+	// LogLevelDebug enables log output at DEBUG level.
+	LogLevelDebug
+	// LogLevelTrace enables log output at TRACE level.
+	LogLevelTrace
+	// LogLevelJSON enables log output at TRACE level in JSON format.
+	LogLevelJSON
+)
+
+// LogLevel is a Terraform log level.
+// As per https://developer.hashicorp.com/terraform/internals/debugging
+type LogLevel int
+
+// ParseLogLevel parses a log level string into a Terraform log level.
+func ParseLogLevel(level string) (LogLevel, error) {
+	switch strings.ToUpper(level) {
+	case "NONE":
+		return LogLevelNone, nil
+	case "ERROR":
+		return LogLevelError, nil
+	case "WARN":
+		return LogLevelWarn, nil
+	case "INFO":
+		return LogLevelInfo, nil
+	case "DEBUG":
+		return LogLevelDebug, nil
+	case "TRACE":
+		return LogLevelTrace, nil
+	case "JSON":
+		return LogLevelJSON, nil
+	default:
+		return LogLevelNone, fmt.Errorf("invalid log level %s", level)
+	}
+}
+
+// String returns the string representation of a Terraform log level.
+func (l LogLevel) String() string {
+	switch l {
+	case LogLevelError:
+		return "ERROR"
+	case LogLevelWarn:
+		return "WARN"
+	case LogLevelInfo:
+		return "INFO"
+	case LogLevelDebug:
+		return "DEBUG"
+	case LogLevelTrace:
+		return "TRACE"
+	case LogLevelJSON:
+		return "JSON"
+	default:
+		return ""
+	}
+}