The name of master user for the client DB instance. MySQL Constraints: 
- Must be 1 to 16 alphanumeric characters.
- First character must be a letter.
- Cannot be a reserved word for the chosen database engine.
- Must be 1 to 30 alphanumeric characters.
- First character must be a letter.
- Cannot be a reserved word for the chosen database engine.
- Must be 1 to 128 alphanumeric characters.
- First character must be a letter.
- Cannot be a reserved word for the chosen database engine.
 Declaration Syntax
 Declaration Syntax| C# | 
public string MasterUsername { get; set; }