toolkit: add file content viewer

[danylo-boiko]

Description

• Added viewer for imported files

AI Description

This PR introduces a new feature for retrieving files by ID, with a focus on agent and conversation files. The changes include:

• Adding a new function, get_file, in src/backend/crud/file.py, which retrieves a file by ID. The function now accepts an optional user_id parameter, allowing for more flexible file retrieval.
• Creating new classes, ConversationFileFull and AgentFileFull, in src/backend/schemas/file.py, to represent conversation and agent files with additional attributes like file_content.
• Modifying the get_files_by_agent_id function in src/backend/services/file.py to return a list of file IDs instead of files. A new function, get_file_ids_by_agent_id, is introduced to retrieve file IDs associated with a specific agent ID.
• Adding new routes in src/backend/routers/agent.py and src/backend/routers/conversation.py to handle file retrieval by ID for agents and conversations, respectively. These routes use the get_file function from the file_crud module.
• Enhancing the src/interfaces/assistants_web/src/cohere-client/client.ts file by adding new methods, getConversationFile and getAgentFile, to retrieve conversation and agent files by ID.
• Introducing new types, AgentFileFull and ConversationFileFull, in src/interfaces/assistants_web/src/cohere-client/generated/types.gen.ts, to represent conversation and agent files with additional attributes.
• Adding new functions, getAgentFileV1AgentsAgentIdFilesFileIdGet and getFileV1ConversationsConversationIdFilesFileIdGet, in src/interfaces/assistants_web/src/cohere-client/generated/services.gen.ts, to retrieve agent and conversation files by ID.
• Creating a new component, FileViewer, in src/interfaces/assistants_web/src/components/UI/FileViewer.tsx, to display file content.
• Enhancing the ConversationPanel component in src/interfaces/assistants_web/src/components/Conversation/ConversationPanel.tsx to handle file viewing and deletion.
• Adding a new hook, useFile, in src/interfaces/assistants_web/src/hooks/use-files.ts, to retrieve agent and conversation files by ID.
• Introducing new tests in src/backend/tests/unit/routers/test_conversation.py to ensure the proper functioning of file retrieval by ID for conversations.

[tianjing-li]

@danylo-boiko Always happy to see more contributions from you.Will review when bandwidth permits