test: Ensure Vaadin add-ons can work without jandex index

[mcollovati]

Description

Added tests to ensure that: 1) Vaadin add-ons without jandex index can be used by setting quarkus.index-dependency entries in application.properties. 2) Vaadin add-ons with jandex index works out of the box

Part of #17

Type of change

• [ ] Bugfix
• [ ] Feature

Checklist

• [X] I have read the contribution guide: https://vaadin.com/docs/latest/guide/contributing/overview/
• [X] I have added a description following the guideline.
• [X] The issue is created in the corresponding repository and I have referenced it.
• [X] I have added tests to ensure my change is effective and works as intended.
• [X] New and existing tests are passing locally with my change.
• [X] I have performed self-review and corrected misspellings.

Additional for Feature type of change

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

[CLAassistant]

All committers have signed the CLA.