fix tls condition for kafka_exporter, issue #6048

[max107]

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PR Description

try to fix issue 6048

Which issue(s) this PR fixes

https://github.com/grafana/alloy/issues/280

Notes to the Reviewer

original kafka exporter allow connect without cert&key pair only with root ca

(sorry, english is not my main language)

UP: checked, it's work

[CLAassistant]

All committers have signed the CLA.

[max107]

in my opinion need to remove this condition completely

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