Add min_disk_size option

[agottlie]

What does this PR do?

Adds the ability to configure the minimum disk size threshold for devices from which to pull metrics.

Motivation

Client Request.

[ruthnaebeck]

👍 for docs

[codecov]

Codecov Report

Merging #4317 into master will increase coverage by 15.98%.
The diff coverage is 88.88%.

Impacted Files	Coverage Δ
disk/tests/test_unit.py	100% <100%> (ø)
disk/datadog_checks/disk/disk.py	84.5% <50%> (ø)
...checks_dev/tests/plugin/test_environment_runner.py
datadog_checks_base/tests/test_similar.py
...g_checks_base/datadog_checks/base/utils/headers.py
...service/datadog_checks/windows_service/__init__.py
..._checks_base/datadog_checks/base/checks/network.py
...v/tests/tooling/config_validator/test_validator.py
...adog_checks_base/datadog_checks/base/utils/date.py
datadog_checks_base/tests/test_kube_leader.py
... and 149 more

[ofek]

@agottlie Thanks for this! I pushed a few commits to fix CI and reverted the legacy path update since I'm about to remove that.