feat: add dashboard component feature flag

[ugur-vaadin]

Description

This PR adds the feature flag for the new Dashboard component.

Related issue

Type of change

• Bugfix
• Feature

Checklist

• I have read the contribution guide: https://vaadin.com/docs/latest/guide/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.
• Enhancement / new feature was discussed in a corresponding GitHub issue and Acceptance Criteria were created.

[sonarcloud]

Quality Gate passed

Issues
13 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

[github-actions]

Test Results

1 156 files  ±0  1 156 suites  ±0   1h 32m 53s ⏱️ -45s
7 498 tests ±0  7 445 ✅ ±0  53 💤 ±0  0 ❌ ±0 
7 823 runs  +5  7 762 ✅ +7  61 💤  - 2  0 ❌ ±0 

Results for commit 1f297e2. ± Comparison against base commit 7ba0f02.