Update index.d.ts

[finntenzor]

Support customize sequelize for typescript.

Checklist

• npm test passes
• tests and/or benchmarks are included
• documentation is changed or added
• commit message follows commit guidelines

Affected core subsystem(s)

Only affected your code tips if you use typescript.

Description of change

Add the Sequelize options declare. It was supported long time ago but not mentioned in the index.d.ts.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 84.37%. Comparing base (78e5193) to head (1ab2e4e).
⚠️ Report is 11 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master      #80      +/-   ##
==========================================
+ Coverage   83.87%   84.37%   +0.50%     
==========================================
  Files           4        4              
  Lines          62       64       +2     
==========================================
+ Hits           52       54       +2     
  Misses         10       10              

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