[RFC] Create or get sentry DSN with terraform

[jvasseur]

Not sure if it is that much of a good idea but I'm proposing it anyway.

Advantages :

• We could easily create a separate DSN for each environment to ease rotating them if necessary.
• No more need to add the DSN manually since it will be fetched by terraform.

Disadvantages :

• There will be one more token to configure to run terraform.