[Backport 2.8] Update 2.8 release notes for security backend

[RyanL1997]

Description

Update 2.8 release notes for security backend

• Category (Enhancement, New feature, Bug fix, Test fix, Refactoring, Maintenance, Documentation)
  Maintenance

Issues Resolved

• Relate Release version 2.8.0 #2785

Is this a backport? If so, please add backport PR # and/or commits #

Testing

[Please provide details of testing done: unit testing, integration testing and manual testing]

Check List

• New functionality includes testing
• New functionality has been documented
• Commits are signed per the DCO using --signoff

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.
For more information on following Developer Certificate of Origin and signing off your commits, please check here.

[codecov]

Codecov Report

Merging #2819 (81d48b1) into 2.8 (570d617) will increase coverage by 0.03%.
The diff coverage is n/a.

@@             Coverage Diff              @@
##                2.8    #2819      +/-   ##
============================================
+ Coverage     61.46%   61.50%   +0.03%     
- Complexity     3380     3383       +3     
============================================
  Files           264      264              
  Lines         18665    18665              
  Branches       3288     3288              
============================================
+ Hits          11472    11479       +7     
+ Misses         5605     5600       -5     
+ Partials       1588     1586       -2     

see 3 files with indirect coverage changes