refactor: redesign logging system for CLI-friendly output (#561)

* refactor: redesign logging system for CLI-friendly output
* refactor: remove ANSI color support from logger
* fix: address PR review feedback

log/level.go

@@ -0,0 +1,42 @@
+package log
+
+// Level defines all the available levels we can log at.
+type Level int32
+
+const (
+	// DebugLevel is the lowest level of logging.
+	// Debug logs are intended for debugging and development purposes.
+	DebugLevel Level = iota + 1
+
+	// InfoLevel is used for user-facing progress and status messages.
+	InfoLevel
+
+	// WarnLevel is used for undesired but relatively expected events,
+	// which may indicate a problem.
+	WarnLevel
+
+	// ErrorLevel is used for undesired and unexpected events that
+	// the program can recover from.
+	ErrorLevel
+
+	// FatalLevel is used for undesired and unexpected events that
+	// the program cannot recover from.
+	FatalLevel
+)
+
+func (l Level) String() string {
+	switch l {
+	case DebugLevel:
+		return "DBG"
+	case InfoLevel:
+		return "INF"
+	case WarnLevel:
+		return "WRN"
+	case ErrorLevel:
+		return "ERR"
+	case FatalLevel:
+		return "FTL"
+	default:
+		return "???"
+	}
+}