feat: add autofocus parameter

[miquelbeltran]

This PR allows to disable autofocus in the LlmChatView.

Currently, the chat input will be focused automatically, to avoid that you can set the list of suggestions. This PR introduces an optional autofocus parameter to override that functionality and force the autofocus on or off.

Closes: #133

Pre-launch Checklist

• I read the Contributor Guide and followed the process outlined there for submitting PRs.
• I read the Tree Hygiene wiki page, which explains my responsibilities.
• I read the Flutter Style Guide recently, and have followed its advice.
• I signed the CLA.
• I listed at least one issue that this PR fixes in the description above.
• I updated/added relevant documentation (doc comments with ///).
• I added new tests to check the change I am making, or this PR is test-exempt.
• All existing and new tests are passing.

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