Update warning about unkown key to use the caller location

[hush-hush]

What does this PR do?

Update warning about unkown key to use the caller location.

Instead of logging:

(pkg/config/viperconfig/viper.go:205 in checkKnownKey) | config key XXX is unknown

We will log, for example:

(cmd/agent/subcommands/run/command.go:535 in startAgent) | config key 'XXX' is unknown

Describe how you validated your changes

Running the CI is enought.

[agent-platform-auto-pr]

Uncompressed package size comparison

Comparison with ancestor a3816f513378e811645a2ac1f5c82ee308b4bd9b

Size reduction summary

package	diff	status	size	ancestor	threshold
datadog-agent-x86_64-rpm	-0.00MB	✅	825.00MB	825.00MB	0.50MB
datadog-agent-x86_64-suse	-0.00MB	✅	825.00MB	825.00MB	0.50MB

Diff per package

package	diff	status	size	ancestor	threshold
datadog-agent-aarch64-rpm	0.00MB	✅	815.86MB	815.86MB	0.50MB
datadog-agent-amd64-deb	0.00MB	✅	815.21MB	815.21MB	0.50MB
datadog-agent-arm64-deb	0.00MB	✅	806.08MB	806.08MB	0.50MB
datadog-dogstatsd-amd64-deb	0.00MB	✅	39.46MB	39.46MB	0.50MB
datadog-dogstatsd-x86_64-rpm	0.00MB	✅	39.54MB	39.54MB	0.50MB
datadog-dogstatsd-x86_64-suse	0.00MB	✅	39.54MB	39.54MB	0.50MB
datadog-dogstatsd-arm64-deb	0.00MB	✅	37.99MB	37.99MB	0.50MB
datadog-heroku-agent-amd64-deb	0.00MB	✅	440.86MB	440.86MB	0.50MB
datadog-iot-agent-amd64-deb	0.00MB	✅	62.14MB	62.14MB	0.50MB
datadog-iot-agent-x86_64-rpm	0.00MB	✅	62.21MB	62.21MB	0.50MB
datadog-iot-agent-x86_64-suse	0.00MB	✅	62.20MB	62.20MB	0.50MB
datadog-iot-agent-arm64-deb	0.00MB	✅	59.36MB	59.36MB	0.50MB
datadog-iot-agent-aarch64-rpm	0.00MB	✅	59.43MB	59.43MB	0.50MB

Decision

✅ Passed