clientGroupsBlock should not be case-sensitive

[onovy]

client IDs in clientGroupsBlock configuration block are matched case-sensitive now. Example:

$ host 192.168.1.1
1.1.168.192.in-addr.arpa domain name pointer UpperCase.test.local

$ cat config.yaml
...
blocking:
  clientGroupsBlock:
    UpperCase.test.local: [ads] # this matches
    uppercase.test.local: [ads] # this doesn't match

DNS is by specs case-insensitive and thus Client ID match from PTR should be case-insensitive.

Thanks.