fix(offloading): Change offloaded nodes datatype to JSON to support 1GB. Fixes #2246

[alexec]

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• Either (a) I've created an enhancement proposal and discussed it with the community, (b) this is a bug fix, or (c) this is a chore.
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Fixes #2246

This can be merged as soon as builds are green and should be manually back-ported to v2.5

[codecov]

Codecov Report

❗ No coverage uploaded for pull request base (master@d309d5c). Click here to learn what that means.
The diff coverage is 0%.

@@            Coverage Diff            @@
##             master    #2250   +/-   ##
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  Coverage          ?   11.35%           
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  Files             ?       71           
  Lines             ?    27983           
  Branches          ?        0           
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  Hits              ?     3178           
  Misses            ?    24400           
  Partials          ?      405

Impacted Files	Coverage Δ
persist/sqldb/migrate.go	0% <0%> (ø)

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