Allow modifying the base url of Groq

[sideef5ect]

Self Checks

• I have searched for existing issues search for existing issues, including closed ones.
• I confirm that I am using English to submit this report (我已阅读并同意 Language Policy).
• [FOR CHINESE USERS] 请务必使用英文提交 Issue，否则会被关闭。谢谢！:）
• Please do not modify this template :) and fill in all the required fields.

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

• Dify allows users to add a Groq API token to use Groq-provided models.
• The current implementation only allows setting the API token.
• Some server environments hosting the Dify backend may have restrictions preventing direct access to the Groq API service.

Proposed Enhancement:

1. Modify the Groq model provider configuration page to include an option for setting a custom API base URL, similar to the OpenAI configuration form.
2. This addition will enable users to specify a proxy server for accessing Groq services when direct access is not possible due to network restrictions.

2. Additional context or comments

No response

3. Can you help us with this feature?

• I am interested in contributing to this feature.