Consolidating the implementation of the prometheus destination

[roda82]

Currently there are two implementations of the Prometheus Destination on PowerAPI:

• DirectPrometheusDB exposing only raw power estimations. It uses sensor and target as labels
• PrometheusDB exposing different values such as mean, std, min and max. It uses sensor and target as labels

In this PR another Prometheus Destination is defined:

• CloudJoulePrometheusDB exposing raw power estimations grouped by targets (i.e., rapl, global, pod). It also processes labels (tags) by considering K8s rules. This implementation uses pod_name, pod_namespace and socket as labels

In this issue is also indicated that there is a conflict between the usage of socket_db as source and prometheus because of their host (127.0.0.1 for socket_db and 0.0.0.0 for prometheus implementation).

A unique basic implementation of prometheus as destination is required exposing just raw estimation metrics. If users need to expose different values with different associated labels, they have to create their own version of the destination.