[Feature][ENG-9691] osfmetrics elastic-6-to-8 migration (part 1)

[aaxelb]

Ticket

• ENG-9691

Purpose

migrate osf-metrics data from elasticsearch6 to elasticsearch8

Changes

• upgrade django-elasticsearch-metrics dependency to support elastic8 and multiple backends at once
• add elastic8 indexes to migrate to
• save new osfmetrics data in both 6 and 8
• add migrate_osfmetrics_6to8 management command to migrate older data

Side Effects

QE Notes

should have no user-visible changes -- worth checking osfmetrics-based features for regressions:

• preprint view/download counts
• project/registration analytics page
• osf metrics api /_/metrics/reports…
• institution dashboard summary and ‘users’ tab

CE Notes

• no django migrations, but should run sync_databases to set up index templates in es8
• manage.py migrate_osfmetrics_6to8
  • without args, compares counts in es6 and es8 (makes no changes)
  • run with --start to schedule celery tasks to do the data migration (and record the start time)
  • add --no-counts to skip counting, in case that's slow
  • check the backround_migration rabbit queue for a more direct view on migration progress -- done when empty

Documentation