enhancement: user agent 2.1

[yenfryherrerafeliz]

Issue #, if available:

Related PR: #3001
It was reverted previously due to integ tests failures. The x-amz-user-agent should have been excluded from metrics gathering.

Description of changes:
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.

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[yenfryherrerafeliz]

Smoke and Integ tests passed:

vendor/bin/behat --format=progress --tags=integ
...................................................................... 70
...................................................................... 140
...................................................................... 210
....................

60 scenarios (60 passed)
230 steps (230 passed)
15m12.41s (44.50Mb)

vendor/bin/behat --format=progress --suite=smoke --tags='~@noassumerole'
...................................................................... 70
...................................................................... 140
...................................................................... 210
..............

112 scenarios (112 passed)
224 steps (224 passed)