feat: add Type function to store interface

[bzp2010]

Please answer these questions before submitting a pull request, or your PR will get closed.

Why submit this pull request?

• Bugfix
• New feature provided
• Improve performance
• Backport patches

What changes will this PR take into?

Add a type function definition to the store interface to help judge which data entity a store manages.

A sub PR of #2099 #2144

Checklist:

• Did you explain what problem does this PR solve? Or what new features have been added?
• Have you added corresponding test cases?
• Have you modified the corresponding document?
• Is this PR backward compatible? If it is not backward compatible, please discuss on the mailing list first

[codecov-commenter]

Codecov Report

Merging #2160 (9aa6118) into master (29e3084) will increase coverage by 0.03%.
The diff coverage is 20.00%.

@@            Coverage Diff             @@
##           master    #2160      +/-   ##
==========================================
+ Coverage   69.42%   69.46%   +0.03%     
==========================================
  Files         188      188              
  Lines        7147     7152       +5     
  Branches      823      823              
==========================================
+ Hits         4962     4968       +6     
+ Misses       1898     1897       -1     
  Partials      287      287              

Flag	Coverage Δ
backend-e2e-test	46.88% <20.00%> (+0.43%)	⬆️
backend-e2e-test-ginkgo	48.80% <20.00%> (-0.31%)	⬇️
backend-unit-test	52.47% <0.00%> (-0.09%)	⬇️
frontend-e2e-test	68.21% <ø> (ø)

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

Impacted Files	Coverage Δ
api/internal/core/store/store.go	88.54% <0.00%> (+0.64%)	⬆️
api/internal/core/store/store_mock.go	0.00% <0.00%> (ø)
api/internal/core/store/storehub.go	71.55% <100.00%> (+0.24%)	⬆️
api/internal/core/storage/etcd.go	51.18% <0.00%> (+1.57%)	⬆️

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