Snapshottable recovery system

[frelon]

Deploy the entire recovery system to the same folder (kernel, initrd and rootfs).

During upgrade deploy to a transitional folder and then switch it with the current recovery system and then delete the old one.

This makes sure we clean up old recovery systems and don't risk mixing systems during upgrade.

Fixes #2021

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 52.11268% with 34 lines in your changes are missing coverage. Please review.

Project coverage is 72.15%. Comparing base (88a9d0c) to head (0004d1b).

Files	Patch %	Lines
pkg/action/upgrade-recovery.go	39.02%	22 Missing and 3 partials :warning:
pkg/elemental/elemental.go	40.00%	5 Missing and 1 partial :warning:
cmd/build-iso.go	0.00%	1 Missing :warning:
pkg/config/config.go	85.71%	0 Missing and 1 partial :warning:
pkg/utils/fs.go	83.33%	1 Missing :warning:

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2032      +/-   ##
==========================================
- Coverage   72.36%   72.15%   -0.21%     
==========================================
  Files          76       76              
  Lines        9021     9043      +22     
==========================================
- Hits         6528     6525       -3     
- Misses       1949     1973      +24     
- Partials      544      545       +1     

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