[metrics-bugs] #23286 [Metrics/CollecTor]: use index-json classes from metrics-lib

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#23286: use index-json classes from metrics-lib
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     Reporter:  iwakeh             |      Owner:  metrics-team
         Type:  enhancement        |     Status:  new
     Priority:  Medium             |  Milestone:  CollecTor 1.3.0
    Component:  Metrics/CollecTor  |    Version:
     Severity:  Normal             |   Keywords:
Actual Points:                     |  Parent ID:
       Points:                     |   Reviewer:
      Sponsor:                     |
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 In order to avoid code duplication replace all classes that are
 duplicating code from metrics-lib.

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Ticket URL: <https://trac.torproject.org/projects/tor/ticket/23286>
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