Add consul 1.9.0 metrics

[coignetp]

What does this PR do?

hashicorp/raft#409 and hashicorp/consul#8271 are merged and released in Consul 1.9.0, we can now easily parse them.

I updated the README instructions for DogStatsD user to have the same tags as the prometheus metrics

Motivation

Additional Notes

Removed some consul environment

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 #8095 (c5151d3) into master (d417e16) will increase coverage by 5.01%.
The diff coverage is 100.00%.

Impacted Files	Coverage Δ
consul/datadog_checks/consul/metrics.py	100.00% <ø> (ø)
consul/tests/common.py	100.00% <100.00%> (ø)
consul/tests/test_integration.py	98.41% <100.00%> (+0.16%)	⬆️
openstack/datadog_checks/openstack/__about__.py
datadog_checks_base/tests/test_metadata.py
openldap/tests/conftest.py
datadog_checks_dev/datadog_checks/dev/env.py
rethinkdb/datadog_checks/rethinkdb/queries.py
external_dns/tests/test_external_dns.py
ibm_db2/tests/common.py
... and 896 more

[kayayarai]

No changes for docs team approval

[florimondmanca]

Looking good! Some suggestions / questions