This change provides:
- A builder class for appending metrics
- Default initialization of a metrics builder within command instantiation
- Wraps user agent logic into a single middleware class
- Adds middlewares into the different features from where metrics can be gather, to acomplish this purpose.

- Move the user agent middleware after the signing step in order to gather signature metrics.
- Add request compression metric gathering.
- Add specific testing for signatures.
- Add specific testing for request compression.
- Add specific testing for s3 encryption clients.
- Add credentials metric gathering logic.
- Add tests for credentials metrics.
- Make existent credentials tests to work with the new field `source`. For example, for tests around profile credentials the source property for credentials MUST be `profile`. The default value for this field is `static`.

- Use static mapping instead of multiple if/else-ifs.
- Remove the endpoint_id metric tracking since it was removed from the spec.
- Make method's name to be verb based.
- Remove the getMetricsBuilder from the CommandInterface.

- Add tests cases to cover credentials sets the correct source when resolved.
- Fix the sso, sso_legacy, and process metrics. They should be all a profile based metric.