Standardize component configuration

[adrianmo]

At this time, MosaicMe components read the configuration in different ways. Which makes it confusing when we are developing and using them.

Let's standardize the way components read their configuration. According to the 12-factor app principles, the configuration should be obtained from environment variables.

Therefore, let's use the existing example.env that is used by the collector and cacher components and extend it with any needed env variable so that it is used by all the components.