Drop one_team_per_user constraint from team_memberships (#5004)

* Drop `one_team_per_user` constraint from `team_memberships`

* Add extra safeguard UPDATE in the migration, just in case

Author: zoldar

priv/repo/migrations/20250129132629_drop_old_one_team_per_user_constraint.exs

@@ -0,0 +1,30 @@
+defmodule Plausible.Repo.Migrations.DropOldOneTeamPerUserConstraint do
+  use Ecto.Migration
+
+  def up do
+    alter table(:team_memberships) do
+      modify :is_autocreated, :boolean, null: false, default: false
+    end
+
+    drop unique_index(:team_memberships, [:user_id],
+           where: "role != 'guest'",
+           name: :one_team_per_user
+         )
+
+    # Might be redundant but redoing it anyway, just to be safe
+    execute """
+    UPDATE team_memberships SET is_autocreated = true WHERE role = 'owner'
+    """
+  end
+
+  def down do
+    create unique_index(:team_memberships, [:user_id],
+             where: "role != 'guest'",
+             name: :one_team_per_user
+           )
+
+    alter table(:team_memberships) do
+      modify :is_autocreated, :boolean, null: false, default: true
+    end
+  end
+end