fix env bug

[wizardlyk]

Describe what this PR does / why we need it

[root@iZbp133pwc8drrt7ra1mkhZ ~]# cat .sealer/Clusterfile 
apiVersion: sealer.io/v2
kind: Cluster
metadata:
  name: my-cluster
spec:
  containerRuntime: {}
  env:
  - RegistryDomain=sea.hub
  - RegistryPort=5000
  - RegistryURL=sea.hub:5000

when dealing with cluster.env , convert string slice to map map[string]string instead of map[string]interface{}.
also, reslove value overwritten problem.

Does this pull request fix one issue?

Fixes #2174

Describe how you did it

Describe how to verify it

Special notes for reviews

[codecov-commenter]

Codecov Report

Patch coverage has no change and project coverage change: -10.84 ⚠️

Comparison is base (006e1db) 19.34% compared to head (a9fa850) 8.50%.

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Additional details and impacted files

@@            Coverage Diff             @@
##             main   #2177       +/-   ##
==========================================
- Coverage   19.34%   8.50%   -10.84%     
==========================================
  Files          96     164       +68     
  Lines        8919   13309     +4390     
==========================================
- Hits         1725    1132      -593     
- Misses       6953   12028     +5075     
+ Partials      241     149       -92     

Flag	Coverage Δ
e2e-tests	8.50% <ø> (?)
unit-tests	?

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see 260 files with indirect coverage changes

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[Stevent-fei]

@wizardlyk add some description

[wizardlyk]

@wizardlyk add some description

done

[kakaZhou719]

LGTM