[vkalapov]

Description:

New cf mta-graph <path/to/mtad.yaml> command that reads a descriptor file,
calls the deploy service's descriptor-based graph endpoint, and prints the
result as DOT notation to stdout. The output can be piped directly to
dot -Tpng | open -f -a Preview for a visual graph.

What changes:

• commands/mta_graph_command.go implements the command: reads the descriptor,
  POSTs to /api/v1/spaces/{spaceGuid}/mtas/graph, prints the DOT response.
• Edges are labelled with the dependency name; apps/services use distinct node
  shapes. rankdir=LR for left-to-right layout.
• Command registered in multiapps_plugin.go.

Issue:

LMCROSSITXSADEPLOY-3717