fix: make "project-id" parameter optional during initialization

[Amnah199]

Related Issues

• fixes #1130

Proposed Changes:

The project is automatically set during authentication using Google Cloud ADCs, which is required for configuration. Therefore, we can make the project-id optional in the component init.

How did you test it?

• Ran existing tests
• Manual testing using examples

Notes for the reviewer

Checklist

• I have read the contributors guidelines and the code of conduct
• I have updated the related issue with new insights and changes
• I added unit tests and updated the docstrings
• I've used one of the conventional commit types for my PR title: fix:, feat:, build:, chore:, ci:, docs:, style:, refactor:, perf:, test:.

[Amnah199]

VertexAIGeminiChatGenerator is already updated. I'll update the tests too 👍

[Amnah199]

@julian-risch updated the examples and also removed project_id from all tests except init. Let me know WDYT.