Use the same password for /metrics in ECS tasks for both prod and dev

[LDiazN]

We can monitor ECS tasks with a Prometheus thanks to this scraping config, but unfortunately we need a different job for both prod and dev because of the basic auth section, the password is different in dev and prod.

In order to scrape metrics for both prod and dev, we would have to create a different job for each environment, duplicating a lot of code

So a possible solution would be to use the same password for both prod and dev (see #186 (comment))

The final result should:

• have a single job block with all the required settings to scrape ECS tasks, both from prod and dev
• allow differentiating the environment with a Prometheus label (environment = dev for example)

[LDiazN]

There's a problem with this task, we need the Prometheus password to be shared between environments but each environment generates its own password:

In the dev environment:
https://github.com/ooni/devops/blob/a4106269f2933fa79c5e1900428533c9e3efd41a/tf/environments/dev/main.tf#L199C5-L212C2

In the prod environment:
https://github.com/ooni/devops/blob/a4106269f2933fa79c5e1900428533c9e3efd41a/tf/environments/prod/main.tf#L221C1-L234C2

Is there any way in which we can access the same credentials in both files?

We could just write the password manually in both environments and change the code to lookup the password instead of actually creating a random password, but this would imply a little more manual maintenance