FaaS metrics - Introduce extra attributes to metrics

[joaopgrassi]

In #88 (comment) we discussed and aligned that all existing FaaS metrics are related to the FaaS itself and not by whoever is invoking them (clients).

Because of this, the conventions were modified and the attributes faas.invoked_name, faas.invoked_provider and faas.invoked_region were removed as those were supposed to be recorded on metrics captured by clients.

This in turn made the metrics only have the faas.trigger attribute. It was proposed that we recorded also the following attributes on all the FaaS metrics:

• faas.name
• cloud.provider
• cloud.region

We should update the metrics and add the aforementioned attributes.

[jviau]

For cloud.* attributes can we instead just say that all FaaS telemetry may include the cloud resource section? https://github.com/open-telemetry/semantic-conventions/blob/main/model/resource/cloud.yaml

[joaopgrassi]

For cloud.* attributes can we instead just say that all FaaS telemetry may include the cloud resource section? main/model/resource/cloud.yaml

We have every attribute listed and try to move away from such wording, better to be explicit. So, the attributes need to be added one by one in the yaml file I'm afraid.