MCP Gateway spec does not allow container volume mount points to be specified

Recent changes to the MCP Gateway do not allow it to configure the volume mounts and other configuration for the backend mcp server containers that it launches.

We need a more structured way to specify these options in the json config passed to the MCP Gateway.

https://github.com/githubnext/gh-aw/blob/main/docs/src/content/docs/reference/mcp-gateway.md