[AND-147] Fix keyboard not closing when opening attachment picker menu and make this behaviour customizable.

[VelikovPetar]

🎯 Goal

The PR introduces a way of configuring different keyboard behaviours (at the movement it is only closeKeyboardOnAttachmentPickerOpen, but it can be extended in the future). The default behaviour is to close the keyboard, so the PR also addresses the issue that the keyboard wasn't closed when opening the attachments picker from the MessagesScreen.

🛠 Implementation details

• Implement new StreamKeyboardConfiguration class which allows customisation of different keyboard behaviours.
• Provide the StreamKeyboardConfiguration via the ChatTheme
• Ensure the keyboard is closed in the AttachmentsPickerMenu (if instructed by the StreamKeyboardConfiguration)

🎨 UI Changes

Before	After
before.mp4	after.mp4

🧪 Testing

1. Open compose sample app
2. Open a chat
3. Tap on the input field so that the keyboard is opened
4. Tap on the attachments button (while the keyboard is open)
5. The keyboard should be closed when the attachment picker is opened

☑️Contributor Checklist

General

• I have signed the Stream CLA (required)
• Assigned a person / code owner group (required)
• Thread with the PR link started in a respective Slack channel (#android-chat-core or #android-chat-ui) (required)
• PR targets the develop branch
• PR is linked to the GitHub issue it resolves

Code & documentation

• Changelog is updated with client-facing changes
• New code is covered by unit tests
• Comparison screenshots added for visual changes
• Affected documentation updated (KDocs, docusaurus, tutorial)

☑️Reviewer Checklist

• UI Components sample runs & works
• Compose sample runs & works
• UI Changes correct (before & after images)
• Bugs validated (bugfixes)
• New feature tested and works
• Release notes and docs clearly describe changes
• All code we touched has new or updated KDocs

🎉 GIF

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