[exporter/kafka] move kafka configures authentication to internal pkg

[sakulali]

Component(s)

exporter/kafka

Is your feature request related to a problem? Please describe.

Function kafkaexporter.ConfigureAuthentication is referenced by the kafkametricsreceiver and kafkareceiver packages as shown below. We can extract that and place it in an internal package so that the references become clearer.
Additionally, we can fix this error when use checkapi tool(go run cmd/checkapi/main.go .):

2023/09/25 15:37:17 exporter/kafkaexporter has more than one function: "ConfigureAuthentication,NewFactory,WithLogsMarshalers,WithMetricsMarshalers,WithTracesMarshalers"
exit status 1

Describe the solution you'd like

Before the adjustment, the directory structure:
exporter/kafkaexporter
├── authentication.go
├── authentication_test.go
├── internal
│ ├── awsmsk
│ │ ├── doc.go
│ │ ├── iam_scram_client.go
│ │ └── iam_scram_client_test.go
├── scram_client.go

After the adjustment, the directory structure (add new directory internal/kafka):
internal/kafka
├── Makefile
├── authentication.go
├── authentication_test.go
├── awsmsk
│ ├── doc.go
│ ├── iam_scram_client.go
│ └── iam_scram_client_test.go
├── go.mod
├── go.sum
├── metadata.yaml
└── scram_client.go

Describe alternatives you've considered

No response

Additional context

No response

[github-actions]

Pinging code owners:

• exporter/kafka: @pavolloffay @MovieStoreGuy

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[pavolloffay]

+1