[fetchCA] Add CustomAudienceNameValidator

This is part of a series of changes to add independent validators for each field of a Custom Audience. The goal is to be able to test any field independent of which representation of a Custom Audience it is a part of.

Test: atest AdServicesServiceCoreUnitTests

Bug: 283857101

Change-Id: I0f8177f5dd8c2a389ae4197cbc7314841474f913
2 files changed