minor #371 [AI Bundle] Add Brave search tool service definition (daFish)

This PR was merged into the main branch.

Discussion
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[AI Bundle] Add Brave search tool service definition

| Q             | A
| ------------- | ---
| Bug fix?      | no
| New feature?  | no <!-- please update src/**/CHANGELOG.md files -->
| Docs?         | yes <!-- required for new features -->
| Issues        | not applicable <!-- prefix each issue number with "Fix #", no need to create an issue if none exist, explain below instead -->
| License       | MIT

Small doc change for the bundle: adds the service definition for the Brave search tool.

Commits
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3a3f19e Add brave search tool service definition in docs

Author: chr-hertel

src/ai-bundle/doc/index.rst

@@ -172,6 +172,8 @@ To use existing tools, you can register them as a service:
         Symfony\AI\Agent\Toolbox\Tool\Firecrawl:
           $endpoint: '%env(FIRECRAWL_ENDPOINT)%'
           $apiKey: '%env(FIRECRAWL_API_KEY)%'
+        Symfony\AI\Agent\Toolbox\Tool\Brave:
+          $apiKey: '%env(BRAVE_API_KEY)%'
 
 Custom tools can be registered by using the ``#[AsTool]`` attribute::