Gracefully skip quantile-less summary metrics

[florimondmanca]

What does this PR do?

Handle summary metrics that don't have a quantile by skipping them to prevent crashing.

Motivation

In a customer's setup, a system is submitting summary metrics without a quantile, eg:

# HELP resilience4j_circuitbreaker_calls Total number of successful calls
# TYPE resilience4j_circuitbreaker_calls summary
resilience4j_circuitbreaker_calls_count{kind="ignored",name="mood",} 0.0
resilience4j_circuitbreaker_calls_sum{kind="ignored",name="mood",} 0.0
resilience4j_circuitbreaker_calls_count{kind="failed",name="mood",} 0.0
resilience4j_circuitbreaker_calls_sum{kind="failed",name="mood",} 0.0
# vvv
resilience4j_circuitbreaker_calls{kind="not_permitted",name="sapi",} 0.0
resilience4j_circuitbreaker_calls{kind="not_permitted",name="mood",} 0.0
# ^^^

Currently this makes the check crash with a KeyError, meaning that the rest of metrics is not submitted which is a major pain point.

Additional Notes

We can look at how what to do with quantile-less metrics later.

Review checklist (to be filled by reviewers)

• Feature or bugfix MUST have appropriate tests (unit, integration, e2e)
• PR title must be written as a CHANGELOG entry (see why)
• Files changes must correspond to the primary purpose of the PR as described in the title (small unrelated changes should have their own PR)
• PR must have changelog/ and integration/ labels attached

[codecov]

Codecov Report

Merging #6909 into master will decrease coverage by 1.37%.
The diff coverage is n/a.

Impacted Files	Coverage Δ
disk/tests/common.py	64.28% <0.00%> (-35.72%)	⬇️
disk/tests/conftest.py	85.71% <0.00%> (-11.43%)	⬇️
disk/datadog_checks/disk/disk.py	83.66% <0.00%> (-3.59%)	⬇️
disk/tests/test_filter.py	96.45% <0.00%> (-3.55%)	⬇️
elastic/tests/test_config.py
consul/tests/test_integration.py
...atadog_checks/base/checks/prometheus/base_check.py
oracle/datadog_checks/oracle/__init__.py
mesos_master/tests/test_integration_e2e.py
system_core/tests/test_integration.py
... and 703 more