feat: Update API usage notifications thresholds

[zachaysan]

Changes

Fixes https://github.com/Flagsmith/flagsmith/issues/4231

Update API usage notifications thresholds for sending notifications to Flagsmith staff and admins.

How did you test this code?

Relied on existing tests for the underlying logic.

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3 Ignored Deployments

| Name | Status | Preview | Comments | Updated (UTC) | | :--- | :----- | :------ | :------- | :------ | | **docs** | ⬜️ Ignored ([Inspect](https://vercel.com/flagsmith/docs/svpaXg9QYX4wPN9ufgLXnYUF9pfD)) | [Visit Preview](https://docs-git-feat-upgradenotificationvalues-flagsmith.vercel.app) | | Jun 26, 2024 6:12pm | | **flagsmith-frontend-preview** | ⬜️ Ignored ([Inspect](https://vercel.com/flagsmith/flagsmith-frontend-preview/2sneQHAixJDpc4rQGDDPpeBR8qNP)) | [Visit Preview](https://flagsmith-frontend-preview-git-feat-upgradenot-52bafc-flagsmith.vercel.app) | | Jun 26, 2024 6:12pm | | **flagsmith-frontend-staging** | ⬜️ Ignored ([Inspect](https://vercel.com/flagsmith/flagsmith-frontend-staging/HtGTKoAytLsYJUsB6uuXnvVgAnf3)) | [Visit Preview](https://flagsmith-frontend-staging-git-feat-upgradenot-b6fc70-flagsmith.vercel.app) | | Jun 26, 2024 6:12pm |

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Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 96.57%. Comparing base (ca2b13b) to head (739a2bd). Report is 2 commits behind head on main.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #4255 +/- ## ======================================= Coverage 96.57% 96.57% ======================================= Files 1190 1191 +1 Lines 38804 38809 +5 ======================================= + Hits 37476 37481 +5 Misses 1328 1328 ```

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