Use consistent formatting for boolean values

[mx-psi]

What does this PR do?

• Have a consistent format on rendered default values.

Motivation

• If setting default: true on the configuration specification of a check, it will be rendered as default: True, instead of default: true, which is what happens when setting example: true.

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 #7405 into master will decrease coverage by 7.82%.
The diff coverage is 50.00%.

Impacted Files	Coverage Δ
...cks/dev/tooling/configuration/consumers/example.py	98.71% <50.00%> (ø)
teamcity/datadog_checks/teamcity/teamcity.py
etcd/tests/test_integration.py
couch/tests/test_unit.py
nginx/tests/test_unit.py
kubelet/tests/test_prometheus.py
proxysql/datadog_checks/proxysql/__init__.py
...tadog_checks/rethinkdb/document_db/transformers.py
mapr/datadog_checks/mapr/utils.py
system_core/tests/test_integration.py
... and 788 more