Add qat principles to segas

[Dineshtj]

Is this pull request a content or a code change? (Please fill in the relevant section and delete the other)

Code change

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Content change

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• [x ] Content does not include any code or configuration changes (excluding frontmatter information)
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[Dineshtj]

Hey Code owners (cc @GraemeSutherlandHO ) , I have added the QAT Principles to the list of SEGAS principles. This is a content change. I have tested the page locally and ran the E2E cypress tests for accessibility. Looks good. Can you please approve?