docs: Add new notation-validation sample policy

[byronchien]

Description

What this PR does / why we need it:

This change adds a sample policy and constraint that matches the default notation validation behavior of "at least one signature must pass verification".

Which issue(s) this PR fixes (optional, using fixes #<issue number>(, fixes #<issue_number>, ...) format, will close the issue(s) when the PR gets merged):

#819

Type of change

Please delete options that are not relevant.

• This change requires a documentation update

How Has This Been Tested?

Please describe the tests that you ran to verify your changes. Please also list any relevant details for your test configuration

• Test A
• Test B

Checklist:

• Does the affected code have corresponding tests?
• Are the changes documented, not just with inline documentation, but also with conceptual documentation such as an overview of a new feature, or task-based documentation like a tutorial? Consider if this change should be announced on your project blog.
• Does this introduce breaking changes that would require an announcement or bumping the major version?
• Do all new files have appropriate license header?

Post Merge Requirements

• MAINTAINERS: manually trigger the "Publish Package" workflow after merging any PR that indicates Helm Chart Change

[codecov]

Codecov Report

Patch and project coverage have no change.

Comparison is base (3714f30) 53.57% compared to head (ee5a2b9) 53.57%.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #823   +/-   ##
=======================================
  Coverage   53.57%   53.57%           
=======================================
  Files          62       62           
  Lines        3679     3679           
=======================================
  Hits         1971     1971           
  Misses       1500     1500           
  Partials      208      208           

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