Inconsistency in email salutation

Problem

In https://gitlab.com/gitlab-org/customers-gitlab-com/-/merge_requests/11923+, the html tag for the email salutation rendering was updated to be consistent through all existing emails. While updating those, another inconsistency was noticed in how we greet the user. It's a mix of Hello <full_name/first_name> or Dear <full_name>. The majority seems to use the full name (first name + last name) while a couple of email use the first name only. The greeting word is also different and changes between Hello and Dear.

Proposal

Create consistency in the emails on how we greet customers. Update the greeting to:

Hello <full_name>

Result

Consistency within the email salutation.