exporter: add field alias for count(*) func

[liubin]

Thank you for contributing to Harbor!

Comprehensive Summary of your change

Add an alias so that orm can parse the column name regardless of
the type and version of the database.

Issue being fixed

Fixes #(issue)

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• Well Written Title and Summary of the PR
• Label the PR as needed. "release-note/ignore-for-release, release-note/new-feature, release-note/update, release-note/enhancement, release-note/community, release-note/breaking-change, release-note/docs, release-note/infra, release-note/deprecation"
• Accepted the DCO. Commits without the DCO will delay acceptance.
• Made sure tests are passing and test coverage is added if needed.
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[codecov]

Codecov Report

Merging #18840 (35f4caa) into main (7ed1920) will decrease coverage by 0.02%.
Report is 2 commits behind head on main.
The diff coverage is n/a.

❗ Current head 35f4caa differs from pull request most recent head 970cf54. Consider uploading reports for the commit 970cf54 to get more accurate results

@@            Coverage Diff             @@
##             main   #18840      +/-   ##
==========================================
- Coverage   67.38%   67.37%   -0.02%     
==========================================
  Files         993      993              
  Lines      108894   108894              
  Branches     2751     2751              
==========================================
- Hits        73381    73370      -11     
- Misses      31566    31582      +16     
+ Partials     3947     3942       -5     

Flag	Coverage Δ
unittests	67.37% <ø> (-0.02%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

Files Changed	Coverage Δ
src/pkg/exporter/project_collector.go	28.43% <ø> (ø)

... and 7 files with indirect coverage changes

[wy65701436]

lgtm

[chlins]

@liubin Hi, the output of the original and new SQL is same in my environment, you mentioned that the original SQL will always got 0 count, how did you reproduce that?

[liubin]

@chlins Sorry I'm using oceanbase, it needs alias to let the beego orm to parse the filed name correctly.

I updated the commit message and description of this PR.

[chlins]

lgtm