Add new metrics for Redis

[tony612]

These metrics are defined from 1.10.0 https://www.envoyproxy.io/docs/envoy/v1.10.0/configuration/network_filters/redis_proxy_filter#config-network-filters-redis-proxy

What does this PR do?

Add support for Redis metrics in new(>=1.10) Envoy version

Motivation

The current version doesn't support these new metrics

Additional Notes

https://www.envoyproxy.io/docs/envoy/v1.10.0/configuration/network_filters/redis_proxy_filter#config-network-filters-redis-proxy

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 #4946 into master will increase coverage by 6.97%.
The diff coverage is n/a.

Impacted Files	Coverage Δ
envoy/datadog_checks/envoy/metrics.py	100% <ø> (ø)	⬆️
...checks_dev/tests/plugin/test_environment_runner.py
riakcs/datadog_checks/riakcs/riakcs.py
oracle/tests/test_oracle.py
...r/datadog_checks/openstack_controller/__about__.py
twistlock/datadog_checks/twistlock/twistlock.py
linkerd/datadog_checks/linkerd/linkerd.py
...oller/datadog_checks/openstack_controller/utils.py
istio/tests/test_e2e.py
gitlab_runner/tests/test_integration.py
... and 812 more

[ofek]

@tony612 Awesome job, thanks!