Migrate reactions when migrating repository from github

[lunny]

• Template change, don't think migrator is the reaction author.
• Unit tests
• Update original author id when user connected external user account.

An issue migrated from go-gitea/test_repo#2 as below:

[lunny]

blocked by #9693

[6543]

Migration[122]: Add original informations for reactions
--
364 | migration_test.go:225:
365 | Error Trace:	migration_test.go:225
366 | migration_test.go:244
367 | Error:      	Received unexpected error:
368 | migrate: do migrate: Cannot add a NOT NULL column with default value NULL
369 | Test:       	TestMigrations/Migrate-sqlite3-1.7.0

[codecov-io]

Codecov Report

❗ No coverage uploaded for pull request base (master@4e566df). Click here to learn what that means.
The diff coverage is 32.36%.

@@            Coverage Diff            @@
##             master    #9599   +/-   ##
=========================================
  Coverage          ?   42.16%           
=========================================
  Files             ?      603           
  Lines             ?    78834           
  Branches          ?        0           
=========================================
  Hits              ?    33243           
  Misses            ?    41520           
  Partials          ?     4071

Impacted Files	Coverage Δ
models/migrations/migrations.go	1.3% <ø> (ø)
modules/migrations/base/pullrequest.go	0% <ø> (ø)
models/user.go	50.46% <0%> (ø)
models/issue.go	54.81% <0%> (ø)
routers/repo/issue.go	38.01% <0%> (ø)
models/migrate.go	0% <0%> (ø)
models/migrations/v123.go	0% <0%> (ø)
modules/migrations/gitea.go	6.89% <0%> (ø)
models/external_login_user.go	21.29% <0%> (ø)
routers/api/v1/repo/issue_reaction.go	75.27% <100%> (ø)
... and 3 more

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[sapk]

Oh sorry @6543, I didn't see your comment.

[sapk]

Can you confirm that it was fixed by 6ac563a ?