Enable to download a csv file

[eukaryo]

Contributor License Agreement

This repository (optuna-dashboard) and Goptuna share common code.
This pull request may therefore be ported to Goptuna.
Make sure that you understand the consequences concerning licenses and check the box below if you accept the term before creating this pull request.

• I agree this patch may be ported to Goptuna by other Goptuna contributors.

Reference Issues/PRs

I will take over this PR:
#648

What does this implement/fix? Explain your changes.

• added a function to make a csv file in backend.
• added a button to download the file in frontend. (in the bottom of TrialTable page)

[codecov]

Codecov Report

Attention: 40 lines in your changes are missing coverage. Please review.

Comparison is base (9e314a9) 67.20% compared to head (3c11fb7) 66.13%.
Report is 19 commits behind head on main.

Files	Patch %	Lines
optuna_dashboard/_app.py	9.09%	40 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #722      +/-   ##
==========================================
- Coverage   67.20%   66.13%   -1.07%     
==========================================
  Files          35       35              
  Lines        2293     2336      +43     
==========================================
+ Hits         1541     1545       +4     
- Misses        752      791      +39     

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[c-bata]

@eukaryo Thank you for your pull request! I took a brief look at the PR and it seems like the changes made by RuTiO2le also appear as a patch written by you. Could you fetch the RuTiO2le:code-fix/download_csv branch and make additional changes on top of that?

$ gh pr checkout 648
$ vim ... # Add changes
$ git add .
$ git commit
$ git push eukaryo code-fix/download_csv

[eukaryo]

Sorry, I see. I close this PR and create another one.