[Security] 9.0.1 release notes

[nastasha-solomon]

Description

Makes several changes:

• Adds release notes for 9.0.1 ([Security] Release notes for 8.17.6, 8.18.1, and 9.0.1 security-docs#6798).
• Updates the known issue description for the bug that forces prebuilt rules to update if the user creates a new Defend integration policy ([REQUEST]: Add known issue about loosing rule actions, exceptions, and customizations when user installs an Elastic Defend integration policy #1094).
• Adds known issue descriptions for Endpoint bugs that were discovered in 9.0.0 and fixed in 9.0.1.
• Makes minor adjustments to the template to ensure the version numbers in anchors are formatted correctly.

Preview

Elastic Security release notes

[yctercero]

@nastasha-solomon could we add in a note on this PR as a bug fix. Something like:

ES|QL rules can now function with queries taking longer than 5 minutes to complete.

cc @marshallmain @vitaliidm

[gabriellandau]

Two small issues. No blockers.

[jmikell821]

One tiny nit, then good to go! 🚢