chore: add SECURITY.md

[scotmatson]

Adds a vulnerability disclosure policy to this repository. Part of a org-wide security policy rollout.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 94.50%. Comparing base (2c364ad) to head (869d776).

Additional details and impacted files

@@           Coverage Diff           @@
##           master     #174   +/-   ##
=======================================
  Coverage   94.50%   94.50%           
=======================================
  Files          12       12           
  Lines        1947     1947           
  Branches      116      116           
=======================================
  Hits         1840     1840           
  Misses         70       70           
  Partials       37       37           

Flag	Coverage Δ
openfeature-provider	53.76% <ø> (ø)

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