feat: add Java API to set Chart mode property

[bwajtr]

Description

The PR vaadin/web-components#8424 introduced a new mode property on <vaadin-chart> component.

This PR adds a Java API to set this mode property. Also deprecates the setTimeline() in favor of setMode() - a change similar to deprecation in the web-component.

Part of #4731

Type of change

• Bugfix
• Feature

Checklist

• I have read the contribution guide: https://vaadin.com/docs/latest/contributing/overview
• I have added a description following the guideline.
• The issue is created in the corresponding repository and I have referenced it.
• I have added tests to ensure my change is effective and works as intended.
• New and existing tests are passing locally with my change.
• I have performed self-review and corrected misspellings.
• [] I have not completed some of the steps above and my pull request can be closed immediately.

Additional for Feature type of change

• Enhancement / new feature was discussed in a corresponding GitHub issue and Acceptance Criteria were created.

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud

[bwajtr]

After a discussion between me, Rolf and Diego we decided to not go in the direction of the mode property, but instead we will make the API more simple by just activating the Gantt chart if the chart type is Gantt.

This makes this PR quite obsolete, because then it boils down to a very few changes on the Java side (basically only by adding the ChartType.GANTT)
Closing this PR and will make the necessary changes directly in this PR:
#6997