[monitoring] Adding backend for influxdb2.x #274

[AbhigyaShridhar]

I realized that this is a big issue and will take some time to be resolved completely so this is the initial code for it

Changes made:

• added another backend in /home/abhigya/Documents/OpenSource/openwisp/monitoring/openwisp-monitoring/openwisp_monitoring/db/backends
• made changes to the init file of backends to now deal with two possible backends and their different requirements
• added initial code for the influxb2.x backend client
• wrote initial code for a method to 'standardize' query results. This will have to be implemented for all the backends in future

[AbhigyaShridhar]

@nemesisdesign @pandafy

Also, as of now I am testing everything I write in a python command line shell. In order to run actual tests and set up a default user, we have to run a docker container setting up the database on a localhost. I am having trouble running the container for influxdb2 (inside the docker-compose file for this project, I ran a container outside the project directory to test my code)

The docker file should look something like this

There are two options to run a docker container for influxdb2, in 'setup' mode and in 'upgrade' mode. As per my understanding, when a user chooses influxdb2 as a backend, they have already migrated to the db, we don't need the functionality to allow users to migrate. So, we should run the container in 'setup' mode. Please let me know your thoughts on this as well. (however as of now, when I start influxdb2 container in the project directory, it doesn't work as intended and we need to figure out why)