move search to alpha

[Stevent-fei]

Describe what this PR does / why we need it

Support search to view the current list of supported images

1. move search to alpha
2. modify default defaultDomain and defaultRepo

Does this pull request fix one issue?

Describe how you did it

Describe how to verify it

Special notes for reviews

[codecov-commenter]

Codecov Report

Base: 21.44% // Head: 21.44% // No change to project coverage 👍

Coverage data is based on head (fb39482) compared to base (48baeed).
Patch has no changes to coverable lines.

❗ Current head fb39482 differs from pull request most recent head 6256d27. Consider uploading reports for the commit 6256d27 to get more accurate results

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #1902   +/-   ##
=======================================
  Coverage   21.44%   21.44%           
=======================================
  Files          74       74           
  Lines        6891     6891           
=======================================
  Hits         1478     1478           
  Misses       5216     5216           
  Partials      197      197           

Impacted Files	Coverage Δ
pkg/image/reference/util.go	83.78% <ø> (ø)

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[kakaZhou719]

LGTM