feat: add copilot ui-tests generator as an experimental-feature

[manolo]

related to: https://github.com/vaadin/platform/issues/6799

[sonarcloud[bot]]

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 SonarCloud

[github-actions[bot]]

Test Results

1 135 files  ± 0  1 135 suites  ±0   1h 19m 59s :stopwatch: - 8m 15s 7 393 tests ± 0  7 343 :white_check_mark: ± 0  50 :zzz: ±0  0 :x: ±0  7 759 runs  +10  7 699 :white_check_mark: +10  60 :zzz: ±0  0 :x: ±0 

Results for commit 28ebfc2b. ± Comparison against base commit 2c25b821.

[manolo]

Ok, let keep this as a draft for now, we can close later