Provide a way to show (and clear) global credentials available at the agent level

[sangee2004]

Steps to reproduce the problem:

1. Create an agent with any tool that requires authentication like github
2. Enable pre authentication.
3. Remove the tool.
4. Add this tool back

Notice that the tool gets into authenticated state right away without being promoted for creds.

As a user this is confusing that my tool gets authenticated right away since it is not obvious at this time that there is a agent level credential still associated with this agent from step 2.

Expected Behavior:
Display credentials available at the agent level .
Also provide user with the ability to clear these credential.