Resolve "Add external processes for controlling and removing Scaleway resources"

Description

The web application already uses a scheduler to monitor and remove Scaleway resources (in particular rogue servers). The security audit has showed some weaknesses:

• if the web application server crashes, there is no mechanism for controlling Scaleway resources or alerting administrators to fix it.
• the number of authorized VMs is not limited

Changelog

Closes #109 , Closes #67

• Add limitation on the global number of resources that can be used (send email to user)
• Add a threshold for sending email alerts to admins when a certain number of resources has been reached
• Add backend APIs for monitoring and an external program which uses these APIs
• Modify emails with config info (dev, qualif). Production config does not have this info displayed in the email.
• Fix email recipients when visio creation fails

How to test

• Modify the scaleway config to set your own threshold, create the correct number of visios and verify that the email has been sent (and dev info)
• You can also change the alert interval if you want to test it.
• Use external program (monitor.sh) to test new backend apis.

Misc

Email alerts interval is set in tools/wsgi.py to every hour since the last alert.

This list is the things to do at deployment side related to this MR:

• modify qualif/prod configs with these new parameters (limit, threshold)
• add a scheduled job (e.g., twice per day) which executes this external program to check the service availability