Migrations: Use Process Manager to create own Context

[6543]

as title :)

now migration processes will show up in http://localhost:3000/admin/monitor

[zeripath]

Cool So I think we can do even better here actually - if we get the process manager to be the one to make the contexts we can get it to stick the PID in the data context, so we can either avoid registering child processes or better display child processes with their parents.

however, this is a great first step towards moving to make these things cancellable from outside process

[6543]

Backport: #13793

[codecov-io]

Codecov Report

Merging #13792 (2a0ab2d) into master (fd1c351) will decrease coverage by 0.10%.
The diff coverage is 84.21%.

@@            Coverage Diff             @@
##           master   #13792      +/-   ##
==========================================
- Coverage   42.24%   42.13%   -0.11%     
==========================================
  Files         707      707              
  Lines       77123    77130       +7     
==========================================
- Hits        32577    32500      -77     
- Misses      39181    39288     +107     
+ Partials     5365     5342      -23     

Impacted Files	Coverage Δ
modules/git/git.go	40.00% <ø> (ø)
modules/repository/repo.go	43.31% <66.66%> (ø)
modules/task/migrate.go	31.42% <80.00%> (+5.27%)	⬆️
modules/git/repo.go	46.23% <100.00%> (+1.05%)	⬆️
modules/migrations/gitea_uploader.go	6.72% <100.00%> (ø)
models/issue_comment.go	43.50% <0.00%> (-9.22%)	⬇️
modules/notification/ui/ui.go	84.72% <0.00%> (-8.34%)	⬇️
modules/notification/mail/mail.go	33.33% <0.00%> (-5.75%)	⬇️
modules/git/commit.go	49.67% <0.00%> (-3.95%)	⬇️
modules/notification/base/null.go	74.28% <0.00%> (-2.86%)	⬇️
... and 15 more

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[6543]

🚀