feat: implement api for "forgot password?" flow (#14915)

Relates to https://github.com/coder/coder/issues/14232

This implements two endpoints (names subject to change):
- `/api/v2/users/otp/request`
- `/api/v2/users/otp/change-password`

coderd/database/migrations/000261_notifications_forgot_password.down.sql

@@ -0,0 +1 @@
+DELETE FROM notification_templates WHERE id = '62f86a30-2330-4b61-a26d-311ff3b608cf';

coderd/database/migrations/000261_notifications_forgot_password.up.sql

@@ -0,0 +1,4 @@
+INSERT INTO notification_templates (id, name, title_template, body_template, "group", actions)
+VALUES ('62f86a30-2330-4b61-a26d-311ff3b608cf', 'One-Time Passcode', E'Your One-Time Passcode for Coder.',
+        E'Hi {{.UserName}},\n\nA request to reset the password for your Coder account has been made. Your one-time passcode is:\n\n**{{.Labels.one_time_passcode}}**\n\nIf you did not request to reset your password, you can ignore this message.',
+        'User Events', '[]'::jsonb);