community: Migrate Vertex AI Search Retriever from v1beta to v1

[lgesuellip]

PR Description

Hey team, this PR migrates the Vertex AI Search Retriever from v1beta to the stable v1 API.

Type

🧹 Refactoring
✅ Test

Changes

Key changes:

• Updated imports from discoveryengine_v1beta to discoveryengine_v1
• Removed unsupported v1beta features from VertexAISearchRetriever: embedding_spec, ranking_expression, relevance_threshold, personalization_spec, and natural_language_query_understanding_spec
• Removed custom embedding functionality dependent on beta features

Testing

• Modified corresponding tests to exclude beta feature tests for vertex_ai_search.

Thank you Team,

[lgesuellip]

Hey @lkuligin ,

I've added all the changes to support both the stable and beta versions of vertex_ai_search and updated the corresponding tests.

The changes turned out to be larger than expected.
Please let me know if you have any comments or suggestions.

Thanks!

[lgesuellip]

@lkuligin ,

The integration tests are failing, but I’m unable to see the CI log details. Could you help me check?

Thanks so much!

[lgesuellip]

@lkuligin

Please let me know if everything looks good or if there’s anything else needed.
Thank you!

[lgesuellip]

@lkuligin Thank you for the feedback! All the changes pushed.