feat: add spring ai implementation for llmprovider

[ugur-vaadin]

Description

This PR adds SpringAiLLMProvider, which implements the LLMProvider interface.

• Supports both streaming and non-streaming chat models
• Supports Spring Tool annotations
• Has a chat max message count of 30
• Has a maximum tool execution count of 20 per message in order to avoid loops
• Supports image, text, audio, video, and PDF (text content) attachments

Fixes #8469

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

[sonarqubecloud]

Quality Gate passed

Issues
8 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