doc: suggestions to enhance setting up your dev environment tutorial

[viniarck]

Minor suggestions to enhance or facilitate setting up dev environment for new developers:

https://github.com/kytos-ng/documentation/blob/master/tutorials/napps/development_environment_setup.rst

• Recommend to use the flag -E (enable all entities) with kytosd to facilitate having entities enabled by default.
• Make MONGO_USERNAME=mymongouser and MONGO_PASSWORD=mymongopass optional (but highlight the importance for production), we can update the default password to fallback to these values, I've noticed that some folks have difficulty exporting these values to all terminal sections and can end up with auth failures as a result.
• Explain how to drop the database when necessary during development

[viniarck]

Maybe also suggest to disable of_l2ls after initially using it since most likely mef_eline will be the NApp they'll end up using to provision p2p connectivity. mef_eline is one of our most used NApps. Sooner or later developers will usually need to reach out to mef_eline for more advanced connectivity scenarios anyway, so it's probably worth also introducing a brief tutorial explaining how to provision a basic EPL on a ring topology.