Add new integration for Brave Search

[sjrl]

Summary and motivation

We have clients who have implemented a custom brave web-search component for use with Haystack and it would be great to bring this in as a core integration.

Detailed design

We should follow the same style/structure as our existing web search components https://docs.haystack.deepset.ai/docs/websearch e.g. SearchApiWebSearch.

Checklist

If the request is accepted, ensure the following checklist is complete before closing this issue.

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
• A new label named like integration:<your integration name> has been added to the list of labels for this repository
• The labeler.yml file has been updated
• The package has been released on PyPI
• An integration tile with 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