Update to the hashing requirements for Google Customer MAtch - AEP Destination

[Issue in ./help/introduction.md](https://experienceleague.adobe.com/docs/experience-platform/destinations/catalog/advertising/google-customer-match.html?lang=en#hashing-requirements)
The hashing requirements mentions here that the phone numbers need to be mapped into "Phone_E.164 namespace". However we can still set-up the destination without using the namespace since the namespace actually forces the attribute to be an identity which is not ideal for most enterprise customers. Can you please update the documentation to show that formating is requirement but its not necessary to be marked as "Phone_E.164 namespace". The messaging is similar for email as well.

Start with ./help/introduction.md and the Google Customer Match hashing requirements section linked in the issue. Review the phone and email guidance, then update it to distinguish required formatting from optional Phone_E.164 namespace mapping; done means the documentation reflects that distinction for both attributes.

Written by the indexing model from the issue text.