fix metadata disable full scan

[famarting]

The changes in this PR address, but don't fix directly, this issues:

• Bug: cluster admin refresh medatadata report error when set Metadata.Full to false. #2069
• backgroundMetadataUpdater can log ErrNoTopicsToUpdateMetadata repetitively if client.conf.Metadata.Full is false #2630

Also this will be of great help in Dapr: dapr/components-contrib#3247

With this changes now it will be possible to set config.Metadata.Full = false but it would require the user to set a topic via
config.Metadata.InitialTopics = []string{"dummy-topic"} , with this the first request to fetch the metadata will either create that topic if it doesn't exist or it will just fetch its metadata

[github-actions]

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