[CONTINT-1165] Cleaning env vars in config

[gabedos]

What does this PR do?

Sets environment variables that have been consistently used on the Agent for years as known to the config.

Motivation

Reduce unnecessary log warnings on start time on the Agent. This will also make it easier to identify when there are actual issues.

Describe how you validated your changes

N/A. Unit tests cover

[agent-platform-auto-pr]

Uncompressed package size comparison

Comparison with ancestor 70abd234c3950faf793ae73b1276bd6d1dc85c46

Diff per package

package	diff	status	size	ancestor	threshold
datadog-agent-amd64-deb	0.01MB	⚠️	1191.11MB	1191.10MB	140.00MB
datadog-agent-x86_64-rpm	0.01MB	⚠️	1200.42MB	1200.42MB	140.00MB
datadog-agent-x86_64-suse	0.01MB	⚠️	1200.42MB	1200.42MB	140.00MB
datadog-iot-agent-aarch64-rpm	0.00MB	✅	108.89MB	108.88MB	10.00MB
datadog-agent-arm64-deb	0.00MB	✅	935.40MB	935.39MB	140.00MB
datadog-agent-aarch64-rpm	0.00MB	✅	944.69MB	944.69MB	140.00MB
datadog-iot-agent-amd64-deb	0.00MB	✅	113.35MB	113.35MB	10.00MB
datadog-iot-agent-arm64-deb	0.00MB	✅	108.82MB	108.81MB	10.00MB
datadog-iot-agent-x86_64-rpm	0.00MB	✅	113.42MB	113.42MB	10.00MB
datadog-iot-agent-x86_64-suse	0.00MB	✅	113.42MB	113.42MB	10.00MB
datadog-dogstatsd-amd64-deb	0.00MB	✅	78.57MB	78.57MB	10.00MB
datadog-dogstatsd-x86_64-rpm	0.00MB	✅	78.65MB	78.64MB	10.00MB
datadog-dogstatsd-x86_64-suse	0.00MB	✅	78.65MB	78.64MB	10.00MB
datadog-dogstatsd-arm64-deb	0.00MB	✅	55.77MB	55.77MB	10.00MB
datadog-heroku-agent-amd64-deb	0.00MB	✅	505.27MB	505.27MB	70.00MB

Decision

⚠️ Warning

[agent-platform-auto-pr]

Test changes on VM

Use this command from test-infra-definitions to manually test this PR changes on a VM:

inv aws.create-vm --pipeline-id=51846514 --os-family=ubuntu

Note: This applies to commit dc80555