Add label's description as tooltip

[Nhqml]

Comprehensive Summary of your change

Adds a tooltip showing the label's description on artifact-list-page. I believe it is not relevant to show it anywhere else (and from what I've tried it often result in broken UI).

Please find a video of how it looks: https://github.com/goharbor/harbor/assets/48765390/54669aaa-6324-4669-9967-80727fb49e64

Note that I'm a complete noob with Frontend/JS/Angular, therefore please let me know if you believe there is a more elegant way to do this.

Please indicate you've done the following:

• 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.
• Considered the docs impact and opened a new docs issue or PR with docs changes if needed in website repository.

[codecov]

Codecov Report

Merging #19421 (bef4652) into main (f58dc2d) will decrease coverage by 0.07%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##             main   #19421      +/-   ##
==========================================
- Coverage   44.89%   44.83%   -0.07%     
==========================================
  Files         244      244              
  Lines       13416    13417       +1     
  Branches     2752     2752              
==========================================
- Hits         6023     6015       -8     
- Misses       7089     7097       +8     
- Partials      304      305       +1     

Flag	Coverage Δ
unittests	44.83% <100.00%> (-0.07%)	⬇️

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

Files	Coverage Δ
...ponents/label/label-piece/label-piece.component.ts	75.00% <100.00%> (+3.57%)	⬆️

... and 2 files with indirect coverage changes

[AllForNothing]

@Nhqml We use the "eslint" for the UI code format. So you need to run npm run lint_fix to format the code. It will help to pass the "CI / UI_UT"

[AllForNothing]

lgtm