Reinstate bulk sms limit

[whabanks]

Summary | Résumé

This PR reinstates bulk sms validation code that was reverted in this PR due to issues with the added validation firing on bulk emails as well.

Related Issues | Cartes liées

cds-snc/notification-utils#294
cds-snc/notification-admin#1834

Test instructions | Instructions pour tester la modification

1. Send a bulk SMS request via the API
2. Note that an error message indicating the message length is too long, possibly due to custom content.
3. Note that the error message is accompanied by the affected row number.

Release Instructions | Instructions pour le déploiement

Due to dep bumps in Utils 52.2.3, this dep bump PR needs to be merged before this PR can be released.

Reviewer checklist | Liste de vérification du réviseur

• This PR does not break existing functionality.
• This PR does not violate GCNotify's privacy policies.
• This PR does not raise new security concerns. Refer to our GC Notify Risk Register document on our Google drive.
• This PR does not significantly alter performance.
• Additional required documentation resulting of these changes is covered (such as the README, setup instructions, a related ADR or the technical documentation).

⚠ If boxes cannot be checked off before merging the PR, they should be moved to the "Release Instructions" section with appropriate steps required to verify before release. For example, changes to celery code may require tests on staging to verify that performance has not been affected.

[jzbahrai]

Tested this on both admin and API, looks like it works!