[PBE-3749] Implement ChatClient::markThreadUnread operation.

[VelikovPetar]

🎯 Goal

Implement the ChatClient.markThreadUnread operation. It will be used as part of the whole Threads V2 implementation.

🛠 Implementation details

• Extend the MarkUnreadRequest with thread_id filed (as per the api documentation)
• Implement new markThreadUnread (similar to markUnread) methods on ChatClient and ChannelClient

🎨 UI Changes

NA

🧪 Testing

Currently not used

☑️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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