As an MCP server author, I want to declare custom capabilities (such as tools, icons and other metadata), so that clients can understand the available functionality and present or select these capabilities appropriately

[rdimitrov]

Details:

• Design notes - https://docs.google.com/document/d/1g2lWdVNjnOk0K56Zj1zZ3BJaOAHOH1FaegRxpFgdcV4/edit?tab=t.53jwhceb1ev2
• Format - Add proposal for tool definitions in publisher extensions toolhive#2733

[rdimitrov]

Updated the description so it's more generic and handles the icons use case

[rdimitrov]

For the tools and their descriptions, let's follow the format proposed by - stacklok/toolhive#2733

[rdimitrov]

Relevant notes for implementing this - https://docs.google.com/document/d/1g2lWdVNjnOk0K56Zj1zZ3BJaOAHOH1FaegRxpFgdcV4/edit?tab=t.53jwhceb1ev2

[lujunsan]

PR is up for review in #414

[lujunsan]

Closing as done, there's #442 as a followup for docs