Adding new metrics for version 1.7.0 of CoreDNS

[FlorianVeaux]

What does this PR do?

Motivation

Additional Notes

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 #6973 into master will increase coverage by 7.61%.
The diff coverage is 100.00%.

Impacted Files	Coverage Δ
coredns/datadog_checks/coredns/coredns.py	88.00% <100.00%> (+1.04%)	⬆️
coredns/tests/common.py	100.00% <100.00%> (ø)
coredns/tests/conftest.py	97.77% <100.00%> (-0.27%)	⬇️
coredns/tests/test_check.py	100.00% <100.00%> (ø)
...checks_base/tests/stubs/test_aggregator_similar.py
..._checks_base/datadog_checks/base/utils/db/utils.py
amazon_msk/tests/test_unit.py
rethinkdb/datadog_checks/rethinkdb/config.py
consul/tests/conftest.py
...checks_dev/datadog_checks/dev/kube_port_forward.py
... and 851 more