feat(mongo): support migrate virtualKey

[Hieuzest]

Support auto migrating optimizeIndex setting in prepare().
Store table preference in _fields.virtual, cause i don't want to create another meta table.
Support crash consistency, cause this migration can cost minutes for large database.

Also: fix Model.extend when Model::unique will grow everytime plugin-database reload.
(which cause _createIndexes to create duplicate Indexes)

PS. No test available cause I just don't know how and where to create tests for this specific case. Multi threading fails my attempts everytime.

[codecov]

Codecov Report

Merging #33 (e29a09f) into master (ac75782) will increase coverage by 0.13%.
Report is 1 commits behind head on master.
The diff coverage is 98.48%.

@@            Coverage Diff             @@
##           master      #33      +/-   ##
==========================================
+ Coverage   97.90%   98.03%   +0.13%     
==========================================
  Files          23       23              
  Lines        4585     4637      +52     
  Branches     1090     1134      +44     
==========================================
+ Hits         4489     4546      +57     
+ Misses         96       91       -5     

Files Changed	Coverage Δ
packages/mongo/src/index.ts	98.06% <98.46%> (+1.16%)	⬆️
packages/core/src/model.ts	96.93% <100.00%> (ø)

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