Add reply_to_id to onboarding

This updates the onboarding task and example template to allow providing
a `reply_to_id` for each team.

docs/onboarding.md

@@ -21,6 +21,7 @@ teams:
     name: # Name of the team
     email: # Contact email address
     phone: # Contact phone number
+    reply_to_id: # Optional GOV.UK Notify Reply-To UUID
 
 schools:
   team1: [] # URNs managed by a particular team

spec/fixtures/files/onboarding/valid.yaml

@@ -13,6 +13,7 @@ teams:
     name: Team 1
     email: [email protected]
     phone: 07700 900816
+    reply_to_id: 24af66c3-d6bd-4b9f-8067-3844f49e08d0
   team_2:
     name: Team 2
     email: [email protected]

spec/models/onboarding_spec.rb

@@ -31,10 +31,12 @@
       team1 = organisation.teams.find_by!(name: "Team 1")
       expect(team1.email).to eq("[email protected]")
       expect(team1.phone).to eq("07700 900816")
+      expect(team1.reply_to_id).to eq("24af66c3-d6bd-4b9f-8067-3844f49e08d0")
 
       team2 = organisation.teams.find_by!(name: "Team 2")
       expect(team2.email).to eq("[email protected]")
       expect(team2.phone).to eq("07700 900817")
+      expect(team2.reply_to_id).to be_nil
 
       expect(team1.schools).to contain_exactly(school1, school2)
       expect(team2.schools).to contain_exactly(school3, school4)