Update now is triggering reinstallation

[maybeec]

Describe the bug
The update now button on the landing page is causing a reinstallation, which is quite confusing.

To Reproduce
Steps to reproduce the behavior:

1. Select your devonfw instance
2. Click on Update now

Expected behavior
Update now should run an update of the instance installed. Not a new installation.
We might want to add another button to allow a new installation as well.

Screenshots