feat(mcp-chat): implement tool-level filtering using plugin configuration

[MattiaDellOca]

Hey, I just made a Pull Request!

Addresses #8307.

This PR allows an admin to disable specific tools from a MCP Server when using the mcp-chat plugin.

Example configuration:

mcpChat:
  mcpServers:
    - id: kubernetes-server
      name: Kubernetes Server
      npxCommand: 'kubernetes-mcp-server@latest'
      env:
        KUBECONFIG: ${KUBECONFIG}
      disabledTools:
        - 'pods_delete'
        - 'pods_exec'

✔️ Checklist

• A changeset describing the change and affected packages. (more info)
• Added or updated documentation
• Tests for new functionality and regression tests for bug fixes
• Screenshots attached (for UI changes)
• All your commits have a Signed-off-by line in the message. (more info)

[backstage-goalie]

Changed Packages

Package Name	Package Path	Changeset Bump	Current Version
@backstage-community/plugin-mcp-chat-backend	workspaces/mcp-chat/plugins/mcp-chat-backend	minor	v0.8.0