Add SNI Check documentation for English and Portuguese versions

[GabrielAzion]

Related issue: EDU-6651

The SNI Check reference documentation has been created.

What was done

New file created — all confidential client data from the draft (Analise SNI Check.md) was excluded. The public documentation covers:

1. What is SNI — concise explanation of the TLS extension and its relationship to workloads and Certificate Manager.

2. Request routing decision algorithm — the full decision tree rendered as a fenced code block, followed by a reference table explaining each step in plain technical language. The final X509_check_host enforcement step is called out explicitly, including the note that case-insensitive comparison prevents false positives.

3. How to identify if your application is affected — instructs users to monitor for 421 Misdirected Request responses, describes the common connection-reuse scenarios that trigger it, and points to Real-Time Events for investigation.

4. How to fix SNI mismatches — actionable guidance: review Certificate Manager entries, use wildcard or multi-SAN certificates, and correlate 421 events with the host/ssl_server_name fields.

5. Why this enforcement matters — explains the SNI Spoofing threat model and why strict validation is the correct security posture.

Standards applied

• Frontmatter matches the pattern used in origin-shield.mdx (title, description, meta_tags, namespace, permalink).
• Nomenclature updated: Digital Certificates → Certificate Manager; Edge Firewall → Firewall; Azion Edge Platform → Azion Web Platform.
• No confidential data — all specific customer domain names, IP addresses, and internal log samples from the draft were omitted.
• Brand voice — technical and direct, outcome-focused, no forbidden expressions.