[Feature]: Add Search Bar to Documentation Site

[openhands-agent]

What problem or use case are you trying to solve?
The documentation site lacks a search feature, making it difficult to locate specific information quickly, such as GitHub code breadcrumbs.

Describe the UX of the solution you'd like
The user should be able to search for keywords or sections within the documentation and receive relevant results instantaneously.

Do you have thoughts on the technical implementation?
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Describe the alternatives considered
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Additional context
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Issue Created By: Graham Neubig on Slack

[openhands-agent]

OpenHands started fixing the issue! You can monitor the progress here.

[openhands-agent]

An attempt was made to automatically fix this issue, but it was unsuccessful. A branch named 'openhands-fix-issue-6408' has been created with the attempted changes. You can view the branch here. Manual intervention may be required.

Additional details about the failure:
While the technical implementation for search functionality has been added through the Algolia integration, the issue cannot be considered fully resolved because:

1. The solution is incomplete - it requires obtaining Algolia credentials through their DocSearch program before the search functionality will actually work. This is a blocking dependency that prevents immediate use.

2. The core user need ("search for keywords or sections within the documentation and receive relevant results instantaneously") is not yet fulfilled since the search feature is not operational without the credentials.

3. The changes made are preparatory in nature - adding configuration files and documentation for future setup. While these are necessary steps, they don't deliver the working search functionality requested in the issue.

The technical groundwork has been laid correctly through:

• Installation of required packages
• Configuration setup in docusaurus.config.ts
• Documentation for implementation

However, until the Algolia credentials are obtained and configured, users still cannot search the documentation, which was the core problem to be solved. The issue should remain open until the search functionality is fully operational for end users.