ROX-28157: emailsender return 429 status on rate limit hit

[johannes94]

Description

Adds some logic and tests to return 429 rate limited instead of 500 cannot send mail for rate limited requests against emailsender.

Checklist (Definition of Done)

• Unit and integration tests added
• Added test description under Test manual
• Documentation added if necessary (i.e. changes to dev setup, test execution, ...)
• CI and all relevant tests are passing
• Add the ticket number to the PR title if available, i.e. ROX-12345: ...
• Discussed security and business related topics privately. Will move any security and business related topics that arise to private communication channel.
• Add secret to app-interface Vault or Secrets Manager if necessary
• RDS changes were e2e tested manually
• Check AWS limits are reasonable for changes provisioning new resources
• (If applicable) Changes to the dp-terraform Helm values have been reflected in the addon on integration environment

Test manual

CI and local test unit test execution.

[kurlov]

🎉

[openshift-ci]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: johannes94, kurlov

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[johannes94]

/retest