feat(#2610): add github actions output notification provider for drift

[Mallikarjunadevops]

Resolves #2610.
Historically, Digger restricted Drift Detection notifications to either Slack webhooks or GitHub Issues. This Pull Request implements a new native provider to export drift detection results strictly as standard GitHub Actions Outputs ($GITHUB_OUTPUT), allowing downstream CI pipeline steps to securely process the raw results via environment variables.

How

• Added the drift-detection-github-action-output boolean configuration parameter to action.yml.
• Created a GithubActionOutputNotification implementation mirroring the core_drift.Notification interface design.
• Implemented cryptographically-secure randomized 16-byte encoded delimiters to ensure that Terraform's multi-line diffs (driftMessage) write correctly to $GITHUB_OUTPUT without terminating the step boundary.
• Upgraded the Basic and Advanced providers to detect INPUT_DRIFT_DETECTION_GITHUB_ACTION_OUTPUT securely and override behavior prior to faulting back to the configuration error string.

Testing

• Extended cli/pkg/drift/ testing coverage by mocking out $GITHUB_OUTPUT to a temporary directory payload buffer.
• Verified correct multi-line <<EOF boundary string injection and format logic natively via the new github_action_test.go suite to guarantee pipeline host safety.
• Handled backwards compatibility perfectly; the string mapping ignores legacy configurations organically.

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Disclosure: I consulted with an AI assistant to verify GitHub Actions output delimiter formats and scaffold the unit tests for this functionality.

_ reviewed , tested and verified manually._