### What changes were proposed in this pull request?
Currently, `WorkerInfo` is used in many places, and allocationBuckets is only used when its own workers want to collect metrics `SLOTS_ALLOCATED`. If there are lots of workers in the RSS cluster, there may be a certain amount of memory waste, each `WorkerInfo` maintain a Array\[Int](61), so remove it from `WorkerInfo`.
And refactor the metrics `SLOTS_ALLOCATED` from gauge to counter. Originally, this metrics is approximately one hour's total only if there are continuous tasks. Now refactoring it into a counter can reduce the cost of maintaining time windows, including storage and timely expiration data, etc. It can also be more flexibly transformed according to user needs on the prometheus side.
### Why are the changes needed?
Ditto.
### Does this PR introduce _any_ user-facing change?
Yes. metrics_SlotsAllocated_Count metrics change from gauge for 1 hour to a increasing counter.
### How was this patch tested?
Cluster test.
Closes#2078 from onebox-li/improve-SlotsAllocated.
Authored-by: onebox-li <lyh-36@163.com>
Signed-off-by: zky.zhoukeyong <zky.zhoukeyong@alibaba-inc.com>
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