feat: lazily create guarded metrics when first using it

[wenym1]

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What's changed and what's your intention?

Only create create a labeled metrics when we use the metrics for the first time. This will be helpful for connector metrics. For example, currently some iceberg sink related metrics are passed to iceberg sink via SinkMetrics struct. However, we will create a label guarded metrics on these iceberg metrics even though the sink is not iceberg sink, which increases unnecessary labeled metrics.

In this PR, we change to initial the metric when we use the metrics for the firstly via LazyLock.

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[fuyufjh]

Hmmm, the complexity is unnecessary to me. For the specific problem I talked with @chenzl25 today, I think the more straight-forward fix is removing the iceberg_xxx metrics from SinkMetrics to something else such as IcebergMetrics, and then let the IcebergSink to maintain it.

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[fuyufjh]

I think the more straight-forward fix is removing the iceberg_xxx metrics from SinkMetrics to something else such as IcebergMetrics, and then let the IcebergSink to maintain it.

I'd like to try this when I get idle time. Would be nice if you can help @chenzl25 :lark-cry:

[chenzl25]

I think the more straight-forward fix is removing the iceberg_xxx metrics from SinkMetrics to something else such as IcebergMetrics, and then let the IcebergSink to maintain it.

I'd like to try this when I get idle time. Would be nice if you can help @chenzl25 :lark-cry:

Oh, I remember this issue and tried to extract iceberg metric from the sink metrics before but failed because it would cause a circular dependency 🥵 . A big effort is needed to refactor the sink metrics.