Metrics for golang filter don't clean when filer removed from LDS configurations

[wonderflow]

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Title: Metrics for golang filter don't clean when filer remove from LDS configurations

Description:

What issue is being seen? Describe what should be happening instead of
the bug, for example: Envoy should not crash, the expected value isn't
returned, etc.

When I'm implementing golang filters with metrics, I found the metrics defined under LDS http_connection_manager via ConfigCallback (https://github.com/envoyproxy/envoy/blob/main/contrib/golang/common/go/api/filter.go#L312 ) is a global metrics.

I expect it to:

1. Have listener as metrics name, e.g. "listener.0.0.0.0_19001.opa_total_requests: 0".
2. Will be removed and reset along with filter configurations.

But the real behavior is:

1. The metrics name is just what we defined in the function: "opa_total_requests: 0"
2. The metrics is always there even when I remove the go filter, when I added it back, the counter number is still the old value which not being reset.

This seems to me is a potential bug that causing memory leak.

Repro steps:

Include sample requests, environment, etc. All data and inputs
required to reproduce the bug.

I'm using go filter via httn, the way I used is described in this PR: mosn/htnn#827

After plugin built, what I'm doing is:

1. Update LDS with new golang filter that registered metrics via ConfigCallback.
2. Request the filter related LDS and corresponding path to generate metrics.
3. Check ":/status" to see metrics
4. Remove the golang filter from LDS.
5. Check the metrics that we can see the metrics is still there.
6. Add golang filter back, requesting, we were able to see the metrics are increasing again based on the old value.

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Config:

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Logs:

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[KBaichoo]

cc @doujiang24

[doujiang24]

1. Have listener as metrics name, e.g. "listener.0.0.0.0_19001.opa_total_requests: 0".

okay, inherit the stat_prefix seems more reasonable.

2. Will be removed and reset along with filter configurations.

Seems there isn't a way remove a stats.

@StarryVae Could you please take a look?

[StarryVae]

1. Have listener as metrics name, e.g. "listener.0.0.0.0_19001.opa_total_requests: 0".

i also think it is more reasonable to inherit the stat_prefix, and i will submit a PR to support it.

2. Will be removed and reset along with filter configurations.

AFAIK, the metric is just removed with LDS update when you remove the golang filter, and there will be a new metric when you bring the filter back, maybe you can try to wait for several time like 30s or more to ensure the old golang filter config is deleted by envoy. cc @wonderflow