Reorganizes the frontend code related to the calls of settings APIs

[eason9487]

Changes proposed in this Pull Request:

This is one of the preliminaries for the shipping Improvements.

To avoid too many file changes for subsequent PRs, this PR reorganizes the code related to the calls of settings APIs:

• Add the saveSettings action as one of the return values to the useSettings hook and update the related uses.
  • Since they are always used together, and there will be a third use case in the subsequent PR.
• Create a new action syncSettings, add it as one of the return values to the useSettings hook and update the related uses.
  • There will be a third use case of calling to mc/settings/sync API in the subsequent PR.
  • They are often used together.
• Correct the JSDoc description for the saveSettings action.

Detailed test instructions:

1. Go to step 2 of the onboarding flow
   1. Open the Network tab of browser's DevTool
   2. Change the Shipping rates setting
      
   3. Inspect Network tab. Check if there is a request issued to wc/gla/mc/settings API and if the request is successful
   4. Select the Preserve log option on the Network tab
   5. Continue to complete the onboarding flow
   6. Inspect Network tab. Check if there is a request issued to wc/gla/mc/settings/sync API and if the request is successful
2. Go to edit free listing page
   1. Open the Network tab of browser's DevTool
   2. Change the Tax rate or Shipping rates setting
   3. Save changes
   4. Inspect Network tab.
   5. Check if there is a request issued to wc/gla/mc/settings API and if the request is successful
   6. Check if there is a request issued to wc/gla/mc/settings/sync API and if the request is successful
      

Changelog entry

[codecov]

Codecov Report

Attention: Patch coverage is 18.18182% with 9 lines in your changes missing coverage. Please review.

Project coverage is 63.5%. Comparing base (9c3514c) to head (bc91758).
Report is 29 commits behind head on develop.

Files with missing lines	Patch %	Lines
js/src/hooks/useSettings.js	0.0%	4 Missing ⚠️
js/src/pages/edit-free-listings/index.js	0.0%	3 Missing ⚠️
js/src/data/actions.js	0.0%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff            @@
##           develop   #2742     +/-   ##
=========================================
- Coverage     63.5%   63.5%   -0.0%     
=========================================
  Files          337     337             
  Lines         5193    5195      +2     
  Branches      1273    1273             
=========================================
  Hits          3299    3299             
- Misses        1721    1723      +2     
  Partials       173     173             

Flag	Coverage Δ
js-unit-tests	63.5% <18.2%> (-<0.1%)	⬇️

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

Files with missing lines	Coverage Δ
...es/onboarding/setup-stepper/saved-setup-stepper.js	87.2% <100.0%> (ø)
js/src/data/actions.js	15.7% <0.0%> (-0.1%)	⬇️
js/src/pages/edit-free-listings/index.js	2.1% <0.0%> (+<0.1%)	⬆️
js/src/hooks/useSettings.js	20.0% <0.0%> (-5.0%)	⬇️

[tomalec]

Thank you for the changes @eason9487 !
I reviewed the code and run both flows, all LGTM.