[metrics-bugs] #25848 [Metrics/Onionoo]: Replace Gson with Jackson

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#25848: Replace Gson with Jackson
---------------------------------+--------------------------
     Reporter:  iwakeh           |      Owner:  metrics-team
         Type:  enhancement      |     Status:  new
     Priority:  Medium           |  Milestone:
    Component:  Metrics/Onionoo  |    Version:
     Severity:  Normal           |   Keywords:
Actual Points:                   |  Parent ID:  #25815
       Points:                   |   Reviewer:
      Sponsor:                   |
---------------------------------+--------------------------
 This ticket should take the
 [https://gitweb.torproject.org/user/karsten/onionoo.git/commit/?h=task-25815&id=ad9425fd6fae63d2d1da8fc31e5feabba4f71cc9
 proof-of-concept branch] from the parent ticket and replace gson
 thoroughly.
 Steps:
 * remove gson from dependencies
 * adapt existing tests, which check part of the escape/unescape issues
 * look at the possible pitfalls b/c of different escape strategies (cf.
 parent ticket for more)
 * all touched classes should replace string concatenation in log
 statements in a separate commit (a step more towards to Metrics coding
 standards)
 * clean-up proof-of-concept branch to not print stack-traces and the like

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Ticket URL: <https://trac.torproject.org/projects/tor/ticket/25848>
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