Add Cilium version metadata

[ChristineTChen]

What does this PR do?

Upstream PR to cilium has been merged and confirmed

Sample Prometheus output:

# HELP cilium_version Cilium version
# TYPE cilium_version gauge
cilium_version{version="1.6.90"} 0

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

[ChristineTChen]

HOLD until feature is released in a stable build. Currently available to test in cilium v.1.7.0-rc2

[stale]

This pull request has been automatically marked as stale because it has not had activity in the last 30 days. Note that this will not be automatically closed, but the notification will remind us to investigate why there's been inactivity.

[ChristineTChen]

/azp run

[azure-pipelines]

Azure Pipelines successfully started running 2 pipeline(s).

[codecov]

Codecov Report

Merging #5408 into master will increase coverage by 1.88%.
The diff coverage is n/a.

Impacted Files	Coverage Δ
fluentd/tests/test_unit.py
..._checks_base/datadog_checks/base/utils/db/query.py
ceph/tests/common.py
go_expvar/tests/test_integration.py
system_swap/tests/test_system_swap.py
oracle/tests/test_oracle.py
marathon/tests/conftest.py
dns_check/tests/mocks.py
disk/datadog_checks/disk/__init__.py
nginx_ingress_controller/tests/conftest.py
... and 810 more