key property
A key is the required name of the tag. The string value can be from 1 to 128
Unicode characters in length and can't be prefixed with "aws:" or "rds:".
The string can only contain only the set of Unicode letters, digits,
white-space, '_', '.', '/', '=', '+', '-' (Java regex:
"^(\p{L}\p{Z}\p{N}_.:/=+\-
*)$").
Implementation
final String? key;