Update metadata for reporting

Update capitalization and group use within Secure index doc metadata

doc/user/application_security/index.md

 ---
-stage: secure
-group: secure
+stage: Secure
+group: Static Analysis
 info: To determine the technical writer assigned to the Stage/Group associated with this page, see https://about.gitlab.com/handbook/engineering/ux/technical-writing/#assignments
 type: reference, howto
 ---