[Upstream] feat: 增加vertex embedding的支持，修改vertex的模型adapter匹配逻辑

[Sagit-chu]

Synced from upstream PR: songquanpeng#2267

Feature:

1. 改动VertexAI的GetAdaptor逻辑，default增加模型adapter的逻辑，便于适配后续新模型产生
2. 增加VertexAI的Embedding的adapter，支持VertexAI的embedding api

我已确认该 PR 已自测通过，相关截图如下：

[codecov-commenter]

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Codecov Report

Attention: Patch coverage is 5.50459% with 103 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
relay/adaptor/vertexai/embedding/adapter.go	0.00%	68 Missing ⚠️
relay/adaptor/gemini/main.go	0.00%	12 Missing ⚠️
relay/adaptor/vertexai/adaptor.go	0.00%	12 Missing ⚠️
relay/adaptor/vertexai/registry.go	35.29%	11 Missing ⚠️

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