Check the actual bytesize of a Sentry JSON payload

What does this MR do and why?

Fixes #393029 (closed).

Since the bytes size of a JSON payload is different from what DeepSize calculates which is Ruby's object size, this MR changes the size validation by checking both the JSON payload size and, if that passes validation, then checks the size computed by DeepSize.

Screenshots or screen recordings

Screenshots (redacted) of failed requests only. Success requests are still working!

As a follow-up, we could present the distinct error messages to users.

Failed requests

How to set up and validate locally

1. Setup Error Tracking for Sentry host
2. Access errors via Monitor > Error Tracking
3. No errors ✅
4. Tweak RESPONSE_SIZE_LIMIT = 1.megabyte in lib/error_tracking/sentry_client.rb and restart background jobs gdk restart rails-background-jobs
5. Observes errors to show up! ❌

MR acceptance checklist

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• I have evaluated the MR acceptance checklist for this MR.