docs(AWS Bedrock): Add alternative integrations and remove outdated Bedrock models registration

[JGoutin]

Summary

Updates the “Integrate with Amazon Bedrock” documentation to reflect current AWS guidance and to clarify the main OpenAI-compatible integration paths for Open WebUI.

What changed

• Removed the “model registration”/enablement step from the Bedrock Access Gateway section (AWS no longer requires that specific step).
• Added a concise “Integration Options” section plus a feature comparison table for:
  • Bedrock Access Gateway (AWS)
  • LiteLLM (Bedrock provider)
  • stdapi.ai (OpenAI-compatible gateway)
• Added setup guidance for stdapi.ai as an alternative integration path.
• Fixed Open WebUI branding (Open-WebUI => Open WebUI)

Disclosure

I’m the author/maintainer of stdapi.ai.

[pr-validator-bot]

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