feat: Add two new fields to org CodeSecurityConfiguration

[tstollin]

This PR updates support for organization-level code security configurations to match the latest REST API schema.

Specifically, it adds the following fields to CodeSecurityConfiguration in github/orgs_codesecurity_configurations.go:

• dependabot_delegated_alert_dismissal
• secret_scanning_extended_metadata

These fields are documented in the GitHub REST API for creating/updating code security configurations:
https://docs.github.com/en/enterprise-cloud@latest/rest/code-security/configurations?apiVersion=2026-03-10#create-a-code-security-configuration

[gmlewis]

Thank you, @tstollin!
LGTM.
Awaiting second LGTM+Approval from any other contributor to this repo.

cc: @stevehipwell - @alexandear - @zyfy29 - @Not-Dhananjay-Mishra - @munlicode

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 93.71%. Comparing base (9f9ead3) to head (55c9d10).

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #4205   +/-   ##
=======================================
  Coverage   93.71%   93.71%           
=======================================
  Files         209      209           
  Lines       19772    19772           
=======================================
  Hits        18529    18529           
  Misses       1046     1046           
  Partials      197      197           

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[Not-Dhananjay-Mishra]

LGTM