Campaign editor - autofill test email contact with current user

[paolocoppo]

When editing a campaign, we would like to automatically add the current user in the "Test email" block.

[bencroker]

That is already the case, if no test contact is selected. The only thing to be aware of is that a contact must already exist with the same email address as the current user. I’ve improved the wording of this for the next release in https://github.com/putyourlightson/craft-campaign/commit/3d05e9bcc1f6549d152a4b0557897cd641079091.