docs: managed https for tracking domains (TASK-80256)

[viniciusgiles]

TASK-80256

What Changed

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PR Checklist

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All PRs Checklist

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Development Changes Checklist (some checks are automatic github actions and will not be listed here. ie. "all tests pass")

• The appropriate tests are created in cypress/ directory in the root of the project
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Note

Low Risk
Documentation-only change; no product code or behavior is modified (main risk is inaccurate guidance or broken links/images).

Overview
Adds a new Tech Resources article, managed-https-for-tracking-domains.md, documenting SparkPost’s managed TLS certificate option for engagement tracking domains via Let’s Encrypt.

Covers prerequisites and DNS requirements (including V2 endpoint and CAA records), step-by-step enablement for new and existing domains, migration guidance from CDN/proxy setups, certificate status/renewal expectations, troubleshooting, and basic API examples for enabling/checking HTTPS.

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❌ Deploy Preview for support-docs failed.

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Cursor Bugbot has reviewed your changes and found 1 potential issue.

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[cursor]

TODO comment accidentally left in published documentation

Medium Severity

A [TODO: Add screenshot of certificate status display] placeholder was left in the document and will be visible to end users in the published support article. This looks like an internal note that was not meant to ship.