chore: Add text-embedding-005 Vertex model support

What does this merge request do and why?

Adds text-embedding-005 Vertex text embedding model to the list of supported Vertex models since the currently used model (textembedding-gecko@003) is being deprecated on May 24, 2025.

https://cloud.google.com/vertex-ai/generative-ai/docs/model-reference/text-embeddings-api#model_versions

Vertex text embedding model discontinuation on ... (gitlab-org/gitlab#521836 - closed)

Merge request checklist

• Tests added for new functionality. If not, please raise an issue to follow up.
• Documentation added/updated, if needed.