LCORE-1595: Design doc/s for MCP Apps integration

This PR introduces design docs for introducing support for the
MCP Apps extension into Lightspeed core, such that responses from
tools can include interactive UI components, instead of a "text wall
that summarizes complex data"

Signed-off-by: Anik Bhattacharjee <anbhatta@redhat.com>

Author: anik120