feat: use duckduckgo if google search key is not specified

[bytecii]

Related Issue

Closes #1385

Description

• Use duckduckgo if google search key is not specified (as the headless search using google can be easily blocked)
• Fix the issue that Search Engine google api key etc cannot be set to other value

Testing Evidence (REQUIRED)

Search using duckduckgo

Now the google api key can be set to other value including empty

• I have included human-verified testing evidence in this PR.
• This PR includes frontend/UI changes, and I attached screenshot(s) or screen recording(s).
• No frontend/UI changes in this PR.

What is the purpose of this pull request?

• Bug fix
• New Feature
• Documentation update
• Other

Contribution Guidelines Acknowledgement

• I have read and agree to the Eigent Contribution Guideline

[Wendong-Fan]

thanks @bytecii , why we don't use browsertoolkit with headless mode? duckduckgo still has rate limit

[bytecii]

thanks @bytecii , why we don't use browsertoolkit with headless mode? duckduckgo still has rate limit

Do you mean that just let the agent to use the browser toolkit instead of using the function tool? if so I think it's already supported (may need to adjust the system prompt)

[nitpicker55555]

Hi @bytecii, regarding issue #1385, I think we may need to wrap a headless browser toolkit as a search toolkit, since DuckDuckGo still has a low rate limit. Could you take a look at this PR camel-ai/camel#3895? What do you think?