ot::Dns::Name::AppendName() method

Encodes and appends a full name to a message. The @p aName must follow "..", i.e., a sequence of labels separated by dot '.' char. E.g., "example.com", "example.com." (same as previous one), "local.", "default.service.arpa", "." or "" (root). Validates that the @p aName is a valid name format, i.e. no empty labels, and labels are `kMaxLabelLength` (63) characters or less, and the name is `kMaxLength` (255) characters or less.