feat: add a '.toBeEmptyObject()' custom matcher.

[hansal7014]

What changes are being made? (feature/bug)

Adding 'toBeEmptyObject()' custom matcher.

Why are these changes necessary? Link any related issues

Closes #228 by adding a new matcher.

Housekeeping

• Unit tests
• Documentation is up to date
• No additional lint warnings
• Typescript definitions are added/updated where relevant

[codecov]

Codecov Report

Merging #255 (62dade1) into main (a92353f) will increase coverage by 100.00%.
The diff coverage is 100.00%.

❗ Current head 62dade1 differs from pull request most recent head 2a3d3e6. Consider uploading reports for the commit 2a3d3e6 to get more accurate results

@@             Coverage Diff             @@
##           main      #255        +/-   ##
===========================================
+ Coverage      0   100.00%   +100.00%     
===========================================
  Files         0       111       +111     
  Lines         0       563       +563     
  Branches      0        99        +99     
===========================================
+ Hits          0       563       +563     

Impacted Files	Coverage Δ
src/matchers/toBeEmptyObject/index.js	100.00% <100.00%> (ø)
src/matchers/toBeEmptyObject/predicate.js	100.00% <100.00%> (ø)
src/matchers/toBeArrayOfSize/index.js	100.00% <0.00%> (ø)
src/matchers/toThrowWithMessage/predicate.js	100.00% <0.00%> (ø)
src/matchers/toIncludeAllMembers/predicate.js	100.00% <0.00%> (ø)
src/matchers/toBeTrue/index.js	100.00% <0.00%> (ø)
src/matchers/toIncludeAllMembers/index.js	100.00% <0.00%> (ø)
src/matchers/toBeOneOf/predicate.js	100.00% <0.00%> (ø)
src/matchers/toBeTrue/predicate.js	100.00% <0.00%> (ø)
src/matchers/toIncludeSameMembers/predicate.js	100.00% <0.00%> (ø)
... and 101 more

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[SimenB]

thanks!