Make GRAPH_BACKEND the default behavior

[willscott]

currently, GRAPH_BACKEND=true needs to be specified as an environmental variable in order to make the backend requests to an HTTP trustless gateway that we would expect.

• this behavior is not in the example usage on the read me
• this behavior is not flagged when the env var is not set when running the server
• this behavior is more expected at this point by a user.

we should change the default to graph backend, rather than having it as lore.

[rvagg]

this env var also needs to be documented on the README