Firecrawl: Add websearch functionality

[bogdankostic]

Is your feature request related to a problem? Please describe.
In #2859 we added the initial Firecrawl crawler integration, which enables crawling known URLs. However, for many use cases we need to start from a user search query rather than a predefined URL list.

Describe the solution you'd like
Add a component that supports WebSearch queries in the Firecrawl integration. Users should be able to provide search phrases, and the component should return search results as documents.

Describe alternatives you've considered
User can already use websearch functionality using SearchApiWebSearch or SerperDevWebSearch components.

[anakin87]

Tasks

• The code is documented with docstrings and was merged in the main branch
• Docs are published at https://docs.haystack.deepset.ai/
• There is a Github workflow running the tests for the integration nightly and at every PR
• The package has been released on PyPI
• A usage example has been added to https://github.com/deepset-ai/haystack-integrations
• The integration has been listed in the Inventory section of this repo README
• The feature was announced through social media