[metrics-bugs] #21145 [Metrics/ExoneraTor]: adapt ExoneraTor to using metrics-base

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#21145: adapt ExoneraTor to using metrics-base
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     Reporter:  iwakeh              |      Owner:  metrics-team
         Type:  enhancement         |     Status:  new
     Priority:  Medium              |  Milestone:
    Component:  Metrics/ExoneraTor  |    Version:
     Severity:  Normal              |   Keywords:
Actual Points:                      |  Parent ID:
       Points:                      |   Reviewer:
      Sponsor:                      |
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 see #20596

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Ticket URL: <https://trac.torproject.org/projects/tor/ticket/21145>
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