Support backend rendering of plots in the top page

[knshnb]

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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.

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Reference Issues/PRs

Top page version of https://github.com/optuna/optuna-dashboard/pull/778

What does this implement/fix? Explain your changes.

This PR supports the backend rendering of the following three plots.

• [x] pareto front
• [ ] history
• [x] hyperparameter importance
• [x] timeline
• [ ] intermediate values

We need to discuss how to handle includePruned and logScale args to address history and intermediate values plots.

[codecov[bot]]

Codecov Report

Attention: 6 lines in your changes are missing coverage. Please review.

Comparison is base (3880129) 69.71% compared to head (ead77a9) 69.53%. Report is 16 commits behind head on main.

Files	Patch %	Lines
optuna_dashboard/_app.py	57.14%	6 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #805 +/- ## ========================================== - Coverage 69.71% 69.53% -0.18% ========================================== Files 35 35 Lines 2364 2370 +6 ========================================== Hits 1648 1648 - Misses 716 722 +6 ```

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[porink0424]

@knshnb Thank you for your PR! I left some suggestions to fix.

[knshnb]

Thanks for the review! I updated the PR.