Email campaigns: support a Reply-To address

Scope & Context Email campaigns have no Reply-To, so replies always go to the From address. Many teams send campaigns from a dedicated sending domain or subdomain to protect their main domain's reputation, and want replies to reach the rep's normal inbox (e.g. [email protected]). On self-hosted instances with several workspaces this is required: a domain can only be registered in one workspace, so other workspaces have to send from subdomains, and replies to those addresses have no mailbox to land in. Current behavior • The campaign envelope has From, To, Topic and Subject. There is no Reply-To. • MessageCampaign has fromAddress but no reply-to field. • MessageCampaignBatchDeliveryService builds the sendEmailBatch call with from only. Expected behavior • An optional Reply-To row in the campaign envelope, under From. • Replies to a campaign go to the Reply-To address when one is set, and to From otherwise. • Test sends use it too. &#…