Add a setting like 'base_url=llm' to make the host app can be run in subpath of a domian, like www.dify.ai/llm/*

[bnuzhouwei]

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1. Is this request related to a challenge you're experiencing? Tell me about your story.

In many cases, we should intergrate many services in a single domain.

2. Additional context or comments

add a base url, so that got a isolation from others.

3. Can you help us with this feature?

• I am interested in contributing to this feature.