bug fix : ApplyRelabeling change metricName which result in the chan…

[foreverm10]

The relabel function in vminsert has the following bugs

1. Unmatched labels may also be modified, resulting in a large time complexity, causes the service to be unavailable
2. All labels whose labenName is __name__ will become null after Relabel, which will cause the selected label to change after Relabel is enabled, resulting in the change of the route selected by the storage. As a result, storage index writes increase, resulting in service write backlog or even crash

[valyala]

@foreverm10 , kindly ping regarding the missing test case for the fixed issue

[foreverm10]

@foreverm10 , kindly ping regarding the missing test case for the fixed issue

after start the relabel function ,GetStorageIdx()return different storageNodeIdx between { Name: "__name__", Value: "foo" } and { Name: "", Value: "foo", } As a result, the storageNodeIdx change after start the relabel function ,which result in a lot of data is written to new nodes ,storage index writes increase, resulting in service write backlog or even crash @valyala