Make sure that `bool` modifier is also properly wrapped into parens.

While at it, make MetricsQL string marshaling more compact:

- Remove whitespace after `on`, `by`, `without`, `ignoring`, `group_left` and `group_right` modifiers.
- Remove whitespace before `bool` modifier.
- Remove whitespace between items inside `on()`, `by()`, `without()`, `ignoring()`, `group_left()` and `group_right()` modifiers.

Updates https://github.com/VictoriaMetrics/VictoriaMetrics/issues/4422