feat(nest): factory options methods made optional

[Matii96]

the default values are now empty objects

PR Checklist

Please check if your PR fulfills the following requirements:

• Tests for the changes have been added (for bug fixes / features)
• Docs have been added / updated (for bug fixes / features)

What is the current behavior?

Nest options factory requires methods returning empty object for each type of options.

What is the new behavior?

Empty options object is substituted in lib implementation.

[codecov-commenter]

Codecov Report

Merging #15 (2088d29) into main (f0a1d31) will decrease coverage by 0.29%.
The diff coverage is 0.00%.

@@            Coverage Diff             @@
##             main      #15      +/-   ##
==========================================
- Coverage   95.29%   94.99%   -0.30%     
==========================================
  Files          68       68              
  Lines         637      639       +2     
  Branches       97       99       +2     
==========================================
  Hits          607      607              
- Misses         30       32       +2     

Flag	Coverage Δ
unittests	94.99% <0.00%> (-0.30%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
...ckages/nest/lib/feature/mediator.feature.module.ts	67.64% <0.00%> (-2.05%)	⬇️
packages/nest/lib/root/mediator.root.module.ts	78.94% <0.00%> (-4.39%)	⬇️

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