Add zero padding to last read date in client-side code

[KshitijThareja]

Closes #8521

This PR aims to add zero padding to last read date for a book in client-side code.

Testing

Steps to verify:

1. Mark a book as "Already Read". A prompt for a read date will appear below the dropper. Click the "Other" option to manually enter a date.
2. Set a read date of 1 January 2023, and submit the form.
3. You'll see that the day and month will be zero padded wherever expected.

Proof

WorkingSample.mp4

Stakeholders

@jimchamp

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 0% with 2 lines in your changes missing coverage. Please review.

Project coverage is 16.00%. Comparing base (0c123ab) to head (da1a33b).
Report is 1713 commits behind head on master.

Files with missing lines	Patch %	Lines
...nlibrary/plugins/openlibrary/js/check-ins/index.js	0.00%	2 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #8523   +/-   ##
=======================================
  Coverage   16.00%   16.00%           
=======================================
  Files          86       86           
  Lines        4692     4692           
  Branches      822      822           
=======================================
  Hits          751      751           
  Misses       3416     3416           
  Partials      525      525           

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[jimchamp]

Thanks @KshitijThareja! Will merge this once the suggested changes have been made.

[KshitijThareja]

@jimchamp I have made the necessary changes. I should have reviewed my previous submission before making the PR.
I guess this PR can be merged now.

[jimchamp]

Lgtm!