Move away from OS migrations using "zypper migration" in favour of "transactional-update migration"

[ipetrov117]

Currently to achieve an OS migration we use zypper migration from a transactional-update run block (ref here).

We were forced to do this, because the transactional-update migration command did not offer the needed flags for automation and because the correct package version of suseconnect-ng was not present on the machine.

As of a couple of months ago these problems have been fixed:

• Missing flag problems fixed in:
  • transactional-update 4.1.9 version for SLE Micro 5.5
  • transactional-update 4.8.1 version for SLE Micro 6.0
• suseconnect-ng package 1.12.0 version is now present on both SLE Micro 5.5, 6.0 and 6.1, which also fixes the problems we had with this package when doing OS migration.

We should switch to using transactional-update migration now that all the problems around it have been ironed out. This would most likely allow us to better track the upgrade process and fail the upgrade pod if it fails.