feat: add duckduckgo search and enhance the text extraction from the website

[jjyaoao]

Description

Add duckduckgo search and enhance the text extraction from the website.

Motivation and Context

Why is this change required? What problem does it solve?
If it fixes an open issue, please link to the issue here.
You can use the syntax close #15213 if this solves the issue #15213

• I have raised an issue to propose this change (required for new features and bug fixes)

Types of changes

What types of changes does your code introduce? Put an x in all the boxes that apply:

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds core functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Documentation (update in the documentation)
• Example (update in the folder of example)

Implemented Tasks

• Subtask 1
• Subtask 2
• Subtask 3

Checklist

Go over all the following points, and put an x in all the boxes that apply.
If you are unsure about any of these, don't hesitate to ask. We are here to help!

• I have read the CONTRIBUTION guide. (required)
• My change requires a change to the documentation.
• I have updated the tests accordingly. (required for a bug fix or a new feature)
• I have updated the documentation accordingly.

Summary by CodeRabbit

• New Features

  • Enhanced search capabilities across multiple search engines including Google and DuckDuckGo.
  • Introduced a feature to continue search based on user interactions.
  • Improved text extraction from web pages for more accurate summarization.

• Documentation

  • Updated documentation for search functionalities.

• Tests

  • Added tests for the new DuckDuckGo search and summarize functionality.

[Appointat]

@camel-ai/camel-maintainers Hi, could you please review this PR? This PR has been proposed for several months now, and we've made many modifications; it should be close to merging. thanks.

[Wendong-Fan]

docstring format is not unified, can be further polished

[Wendong-Fan]

Dear @camel-ai/camel-maintainers
A kind reminder, we should complete the review of this PR before the end of this sprint, which is in two days.