feat: Copilot plugin

[MarcinVaadin]

Description

Added code required to use AppSec Kit as Copilot plugin.

Tested using:

<dependency>
    <groupId>com.vaadin</groupId>
    <artifactId>copilot-client-free</artifactId>
    <version>24.3-SNAPSHOT</version>
</dependency>

<dependency>
    <groupId>com.vaadin</groupId>
    <artifactId>appsec-kit-starter</artifactId>
    <version>3.0-SNAPSHOT</version>
</dependency>

and with application.property: vaadin.frontend.hotdeploy=true

Current look:

Styling could be improved separately - https://github.com/vaadin/appsec-kit/issues/153

Fixes: https://github.com/vaadin/copilot-internal/issues/343

Type of change

• [ ] Bugfix
• [x] 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.
• [ ] 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

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