Regex change for domainName field

[saikiranakula-amzn]

Description of changes:
Regex validation check if the domainName is up to DNS naming standards
Testing:
int main() {
std::cout << "test regex" << "\n";

//std::cout << "a.com" << "\n";
std::cout << isValidDomain("a.com") << "\n";
//std::cout << isValidDomain("ab.com") << "\n";
std::cout << isValidDomain("ab.toto-abc.com") << "\n"; 
std::cout << isValidDomain("p/") << "\n";
std::cout << isValidDomain("test4.gmsa-pentest.com") << "\n";
std::cout << isValidDomain("-geeksforgeeks.org") << "\n";
std::cout << isValidDomain("contoso.com") << "\n";
std::cout << isValidDomain(".org") << "\n";

return 0;

}
~
"regex.cpp" 49L, 1331B written
[ec2-user@EC2AMAZ-Ll40tS ~]$ g++ -o test regex.cpp
[ec2-user@EC2AMAZ-Ll40tS ~]$ ./test
test regex
test1
test1
fail0
test1
fail0
test1
fail0

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[jamolina]

Approved