FEATURE: send max 200 emails every minute for bulk invites (#7875)

DEV: deprecate `invite.via_email` in favor of `invite.emailed_status`

This commit adds a new column `emailed_status` in `invites` table for
 tracking email sending status.
 0 - not required
 1 - pending
 2 - bulk pending
 3 - sending
 4 - sent

For normal email invites, invite record is created with emailed_status
 set to 'pending'.

When bulk invites are sent invite record is created with emailed_status
 set to 'bulk pending'.

For invites that generates link, invite record is created with
 emailed_status set to 'not required'.

When invite email is in queue emailed_status is updated to 'sending'

Once the email is sent via `InviteEmail` job the invite emailed_status
 is updated to 'sent'.

spec/jobs/invite_email_spec.rb

@@ -27,8 +27,15 @@ describe Jobs::InviteEmail do
         InviteMailer.expects(:send_invite).never
         Jobs::InviteEmail.new.execute(invite_id: invite.id)
       end
+
+      it "updates invite emailed_status" do
+        invite.emailed_status = Invite.emailed_status_types[:pending]
+        invite.save!
+        Jobs::InviteEmail.new.execute(invite_id: invite.id)
+
+        invite.reload
+        expect(invite.emailed_status).to eq(Invite.emailed_status_types[:sent])
+      end
     end
-
   end
-
 end