feat(security): Update SECURITY.md, add security.txt

[bnevis-i]

Removes obsolete information from SECURITY.md and adds a security.txt for inclusion into docker images and snaps.

References: #4151

PR Checklist

Please check if your PR fulfills the following requirements:

• I am not introducing a breaking change (if you are, flag in conventional commit message with BREAKING CHANGE: describing the break)
• I am not introducing a new dependency (add notes below if you are)
• I have added unit tests for the new feature or bug fix (if not, why?) N/A
• I have fully tested (add details below) this the new feature or bug fix (if not, why?) N/A
• I have opened a PR for the related docs change (if not, why?) N/A

Testing Instructions

New Dependency Instructions (If applicable)

[sonarqubecloud]

Kudos, SonarCloud Quality Gate passed!   

0 Bugs
0 Vulnerabilities
0 Security Hotspots
0 Code Smells

No Coverage information
No Duplication information

[codecov-commenter]

Codecov Report

Merging #4407 (83fea74) into main (a219a96) will not change coverage.
The diff coverage is n/a.

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@@           Coverage Diff           @@
##             main    #4407   +/-   ##
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  Coverage   43.66%   43.66%           
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  Files         116      116           
  Lines       10724    10724           
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  Hits         4683     4683           
  Misses       5619     5619           
  Partials      422      422           

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[jim-wang-intel]

LGTM