Feat: support bedrock endpoint configuration with env variable

[oliviamn]

💻 变更类型 | Change Type

• ✨ feat
• 🐛 fix
• ♻️ refactor
• 💄 style
• 👷 build
• ⚡️ perf
• 📝 docs
• 🔨 chore

🔀 变更说明 | Description of Change

1. Add support for Bedrock endpoint setup by using environment variables

📝 补充信息 | Additional Information

add environment variable: AWS_ENDPOINT_URL_BEDROCK_RUNTIME to support bedrock proxy

it resolves the issue(feat request):#4815
user can set environment variable after following the project: https://github.com/jief123/bedrockproxy/blob/main/howto.md

AWS_ENDPOINT_URL_BEDROCK_RUNTIME="https://xxx.cloudfront.net"

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