Updated Vertex credentials

[blublinsky]

Description

Summary
Vertex credential JSON: Supports type: service_account (existing) and type: authorized_user (refresh token + client id/secret, optional token_uri / quota_project_id). Shared helper load_vertex_credentials in ols/src/llms/providers/utils.py validates JSON shape, requires a non-empty type, and applies VERTEX_AI_OAUTH_SCOPES for Vertex.
Single module: GoogleVertexAnthropic lives in google_vertex.py next to GoogleVertex; google_vertex_anthropic.py removed. Registry/tests import both from google_vertex.
Tests: Vertex Gemini + Anthropic coverage consolidated in test_google_vertex.py; test_google_vertex_anthropic.py removed. Provider registry test imports updated.
Docs: docs/ai/providers.md and .ai/spec/how/* updated for module layout and credential file shapes.
Tooling: Bandit exclude_dirs extended with .venv and konflux-artifacts so local scans stay scoped (optional to mention if you want a minimal PR—split if reviewers prefer).

Type of change

• Refactor
• New feature
• Bug fix
• CVE fix
• Optimization
• Documentation Update
• Configuration Update
• Bump-up dependent library
• Bump-up library or tool used for development (does not change the final image)
• CI configuration change
• Konflux configuration change

Related Tickets & Documents

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• PR has passed all pre-merge test jobs.
• If it is a core feature, I have added thorough tests.

Testing

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• How were the fix/results from this change verified? Please provide relevant screenshots or results.

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[xrajesh]

add a case for authorized_user case too ? @blublinsky

[blublinsky]

fixed

[openshift-ci]

@blublinsky: all tests passed!

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