Migrations: Gitlab Add Reactions Support for Issues & MergeRequests

[6543]

as title

include #12693

[codecov-commenter]

Codecov Report

Merging #12695 into master will decrease coverage by 0.03%.
The diff coverage is 0.00%.

@@            Coverage Diff             @@
##           master   #12695      +/-   ##
==========================================
- Coverage   43.33%   43.30%   -0.04%     
==========================================
  Files         645      645              
  Lines       71531    71560      +29     
==========================================
- Hits        30998    30986      -12     
- Misses      35514    35555      +41     
  Partials     5019     5019              

Impacted Files	Coverage Δ
modules/migrations/gitlab.go	1.04% <0.00%> (-0.09%)	⬇️
models/repo_mirror.go	2.38% <0.00%> (-11.91%)	⬇️
modules/cron/tasks_basic.go	87.35% <0.00%> (-3.45%)	⬇️
modules/queue/workerpool.go	56.73% <0.00%> (-3.27%)	⬇️
modules/process/manager.go	72.50% <0.00%> (-2.50%)	⬇️
modules/queue/unique_queue_disk_channel.go	53.84% <0.00%> (-1.54%)	⬇️
services/mirror/mirror.go	18.58% <0.00%> (-1.36%)	⬇️
models/issue_comment.go	53.75% <0.00%> (-0.16%)	⬇️
services/pull/pull.go	41.57% <0.00%> (ø)
modules/indexer/stats/db.go	52.17% <0.00%> (ø)
... and 4 more

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[lunny]

LGTM except for https://github.com/go-gitea/gitea/pull/12695/files#r482700319