[Enh]: Add `mcp` support to `stored-procedure`

[JerryNixon]

What?

Allow an entity of type stored-procedure to be added as a custom MCP tool.

Why?

This would be the easiest way to add a custom tool.

Important

This is just one way to add a custom MCP tool to Data API builder.

How?

This feature depends on these other features:

• [Enh]: Add entity description (metadata) #2834
• [Enh]: Add parameter description (metadata) #2835

Configuration

• The tool name is the entity alias
• The tool description is the entity description
• When custom-tool = true the stored procedure is elevated as a dedicated tool.