Improved environment variable support

[tolbrino]

This PR updates the hoprd image to the latest version in the singapore branch.

Moreover, it adds 2 explicit env vars to be configured by the user:

HOPRD_MAX_BLOCK_RANGE
HOPRD_MAX_RPC_REQUESTS_PER_SEC

And 2 auxiliary env vars which can be used to either add more env vars to the hoprd process or pass on cmdline arguments:

ADDITIONAL_CMDLINE_ARGS
ADDITIONAL_ENVIRONMENT_VARS

Examples uses of these env vars look like this:

ADDITIONAL_CMDLINE_ARGS="--maxRpcRequestsPerSec 100"
ADDITIONAL_ENVIRONMENT_VARS="SOME_SWARM_CONF=10 SOME_OTHER_CONF=34"