[SSL] Mention MDC in advanced certs and point to CF4SaaS (#25777)

* Update index.mdx

Advanced cert only covers the zone and the respective subdomains related to the zone.

* Fix capitalization, define acronym, and cross-link other docs

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Co-authored-by: Rebecca Tamachiro <[email protected]>

Author: omarshariff316

src/content/docs/ssl/edge-certificates/advanced-certificate-manager/index.mdx

@@ -50,6 +50,8 @@ Advanced certificates are not used with [Cloudflare Pages](/pages/) nor [R2](/r2
 
 Advanced certificates are [Domain Validated (DV)](/ssl/concepts/#validation-level). If your organization needs Organization Validated (OV) or Extended Validation (EV) certificates, refer to [Custom certificates](/ssl/edge-certificates/custom-certificates/). <br/>
 
+Advanced certificates do not cover multiple different domains. For multi-domain certificate (MDC), consider the [Cloudflare for SaaS](/cloudflare-for-platforms/cloudflare-for-saas/) product. You can also find further guidance in [Leveraging Cloudflare for your SaaS applications](/reference-architecture/design-guides/leveraging-cloudflare-for-your-saas-applications/).
+
 ## Related resources
 
 <DirectoryListing />