change username in secret when switching rotation mode

[FxKu]

You may want certain users to switch to in-place rotation, but the operator does not set the username when it branches to in-place rotation in the go code. Thus, the username would always stay the same. It needs an extra line secret.Data["username"] = []byte(secretUsername). Another workaround could be to first opt out with the new option introduced with #2528 and add the user to in-place rotation list afterwards.

But, the operator could also be smart enough to detect when the desired username is not a rotation user and allow for immediate rotation. This is what this PR introduces.

It can also work the other way around when switching from in-place rotation to rotation with extra users, like:

	if len(currentUsername) != len(expectedUsername) {
		rotationModeChanged = true

Unlike before, this would kick in any initial rotation immediately an not after the rotation period. However, it makes the current unit tests impossible. A rotation can produce a list of retention user which the operator tries to drop from the database. Database connections will fail in the unit test. So in the scenario switching from in-place to users rotation the user will need to wait for the next rotation data which is stored in secret - like it before.

[jopadi]

👍

[FxKu]

👍