Fix: Skip the non-exist namespaces when there are multiple mongo instance metrics to scrape

[LinPr]

Refer to this issue: #1144

Changes:

1. skip the non-exist namespaces when there are multiple mongo instance metrics to scrape
2. by the way the listAllCollections(ctx, client, collections, nil, true) need to pass collections as the third parameter to reduce the databases and collections to list, wihich can improve the performance

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 65.09%. Comparing base (dc46ed5) to head (28ba21c).
⚠️ Report is 123 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1145      +/-   ##
==========================================
- Coverage   70.88%   65.09%   -5.80%     
==========================================
  Files          28       29       +1     
  Lines        3569     3091     -478     
==========================================
- Hits         2530     2012     -518     
- Misses        904      939      +35     
- Partials      135      140       +5     

Flag	Coverage Δ
agent	65.09% <100.00%> (-5.80%)	⬇️

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