Updated Block List Editor article as per test findings

[eshanrnh]

📋 Description

Addresses user feedback regarding a critical documentation gap in the Block List Editor section. This PR introduces a section detailing how to programmatically create, read, and update Block List content via C# using IContentService and IContentTypeService for Umbraco 17 and 18.

Code snippets generated with the help of Claude. Tested on CMS v17.4.2.

📎 Related Issues (if applicable)

✅ Contributor Checklist

I've followed the Umbraco Documentation Style Guide and can confirm that:

• Code blocks are correctly formatted.
• Sentences are short and clear (preferably under 25 words).
• Passive voice and first-person language (“we”, “I”) are avoided.
• Relevant pages are linked.
• All links work and point to the correct resources.
• Screenshots or diagrams are included if useful.
• Any code examples or instructions have been tested.
• Typos, broken links, and broken images are fixed.

Product & Version (if relevant)

CMS v17 and v18

Deadline (if relevant)

Anytime

📚 Helpful Resources

• 🧾 Umbraco Contribution Guidelines
• ✍️ Umbraco Documentation Style Guide

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