[Improvement] passwordGenerationPolicy support both upper and lower case guaranteed

[lynnleelhl]

something database need strong password, e.g. sqlserver, this is an error I got:

Password validation failed. The password does not meet SQL Server password policy requirements because it is not complex enough. The password must be at least 8 characters long and contain characters from three of the following four sets: Uppercase letters, Lowercase letters, Base 10 digits, and Symbols.

in systemAccounts field, letterCase: MixedCases means possible to have upper or lower case, but not guaranteed to have them both, sometimes I will get a password with all upper case letters, that may fail the initialization

[shanshanying]

@yipeng1030 pls help fix this issue.