fix: include commas in the profile size, handle failure case of profile more than 500kB in size

[yashasvibajpai]

Description

On debugging for the issue, we came across the two pointers addressed here.

1. commas in JSON were unaccounted for in the final size of payload.
2. we will throw an error in case a single profile's size itself crosses the 500 kb threshold set by Klaviyo themselves. Reference

Linear Ticket

Related to INT-2820, INT-2840

Security

• The code changed/added as part of this pull request won't create any security issues with how the software is being used.

[codecov]

Codecov Report

Attention: Patch coverage is 0% with 17 lines in your changes missing coverage. Please review.

Project coverage is 73.25%. Comparing base (18c102f) to head (349310f).
Report is 7 commits behind head on master.

Files with missing lines	Patch %	Lines
...tionmanager/klaviyobulkupload/klaviyobulkupload.go	0.00%	17 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #5241      +/-   ##
==========================================
+ Coverage   73.24%   73.25%   +0.01%     
==========================================
  Files         424      424              
  Lines       59960    59978      +18     
==========================================
+ Hits        43918    43938      +20     
+ Misses      13585    13579       -6     
- Partials     2457     2461       +4     

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[koladilip]

add tests and also add ratelimits in HTTP client

[yashasvibajpai]

Will be handling them now in separate PRs, this PR is mainly a followup to a reported issue