[Request][8.15.4 & 8.16.0] Add RN summary about Defend bug fix

[nastasha-solomon]

Description

See Slack convo for more details.

Background & resources

• PRs: N/A
• Issues/metas: N/A
• Point of contact: @gabriellandau
• Test environments: N/A

Which documentation set does this change impact?

ESS only

ESS release

8.15.4 & 8.16.0

Serverless release

N/A

Feature differences

N/A

API docs impact

N/A

Prerequisites, privileges, feature flags

N/A

[nastasha-solomon]

RNs updated