Add a choice of DB connection establishment

CHANGES:
Changes based on https://mongodb.github.io/node-mongodb-native/3.5/api/

• Added new adapter property databaseConnection(with 2 values to choose from: "connect on startup" or "connect on request"). Detailed description is in the tooltip.

• when "connect on request" mode selected, then adapter goes online (green/green) unconditionally

• made public methods async to simplify code (they did not return anything but just executed passed in callback upon completion anyway)

• fixed set object in reserveNextRecord(...) (it had nested: $set: {$set: {...}})

TEST:
WFs used for test(in both connection modes "connect on startup" and "connect on request"):

mongo-test-3.json

mong-test-1.json

mongo-test-2.json