[Observability] Update SSL settings for lightweight monitors

[alaudazzi]

This PR:

• Adds a new section Supported SSL options for lightweight monitors with the supported keys
• Updates both HTTP and TCP ssl option blocks:
  • Changed type from Heartbeat SSL link to object
  • Added a pointer to the new supported-options section
• Removes Heartbeat SSL doc references in TCP/host wording where they implied broader support.
• Updates SSL examples to use ["TLSv1.2", "TLSv1.3"] for supported_protocols.

Generative AI disclosure

1. Did you use a generative AI (GenAI) tool to assist in creating this contribution?

• Yes
• No

Closes #5261

[github-actions]

✅ Vale Linting Results

No issues found on modified lines!

---

The Vale linter checks documentation changes against the Elastic Docs style guide.

To use Vale locally or report issues, refer to Elastic style guide for Vale.

[github-actions]

🔍 Preview links for changed docs

• solutions/observability/synthetics/configure-lightweight-monitors.md

[florent-leborgne]

LGTM from a docs perspective