fix: clean markdownlint violations in ssl_attributes_extensions.markdown

File was touched to update link text; per project convention, clean all
violations in the changed file: wrap long lines (MD013), add language
identifiers to fenced code blocks (MD040), suppress false-positive emphasis
warning around Liquid include tag (MD037), and drop unnecessary ./ prefixes
from link reference definitions per CONTRIBUTING.md linking rules.

Signed-off-by: Michael Harp <mike@mikeharp.com>

Author: miharp