chore: clean metadata handler for attach command

[qweeah]

What this PR does / why we need it:
This PR is a follow-up of #1578 with minor code change in attach metadata handler.

Please check the following list:

• Does the affected code have corresponding tests, e.g. unit test, E2E test?
• Does this change require a documentation update?
• Does this introduce breaking changes that would require an announcement or bumping the major version?
• Do all new files have an appropriate license header?

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 84.29%. Comparing base (53247dd) to head (90c796c).
Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1584      +/-   ##
==========================================
- Coverage   84.33%   84.29%   -0.04%     
==========================================
  Files         120      120              
  Lines        5413     5413              
==========================================
- Hits         4565     4563       -2     
- Misses        602      604       +2     
  Partials      246      246              

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[shizhMSFT]

LGTM with suggestions