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/dbmem/dbmem.go

@@ -9077,6 +9077,26 @@ func (q *FakeQuerier) UpdateUserGithubComUserID(_ context.Context, arg database.
 	return sql.ErrNoRows
 }
 
+func (q *FakeQuerier) UpdateUserHashedOneTimePasscode(_ context.Context, arg database.UpdateUserHashedOneTimePasscodeParams) error {
+	err := validateDatabaseType(arg)
+	if err != nil {
+		return err
+	}
+
+	q.mutex.Lock()
+	defer q.mutex.Unlock()
+
+	for i, user := range q.users {
+		if user.ID != arg.ID {
+			continue
+		}
+		user.HashedOneTimePasscode = arg.HashedOneTimePasscode
+		user.OneTimePasscodeExpiresAt = arg.OneTimePasscodeExpiresAt
+		q.users[i] = user
+	}
+	return nil
+}
+
 func (q *FakeQuerier) UpdateUserHashedPassword(_ context.Context, arg database.UpdateUserHashedPasswordParams) error {
 	if err := validateDatabaseType(arg); err != nil {
 		return err
@@ -9090,6 +9110,8 @@ func (q *FakeQuerier) UpdateUserHashedPassword(_ context.Context, arg database.U
 			continue
 		}
 		user.HashedPassword = arg.HashedPassword
+		user.HashedOneTimePasscode = nil
+		user.OneTimePasscodeExpiresAt = sql.NullTime{}
 		q.users[i] = user
 		return nil
 	}