[FE] Add SecurityScanning Item to CurrentBranch Tree View

• Add Security scanning TreeView TopNav Item
• Add Unit tests

Implementation Plan

• Add Item to https://gitlab.com/gitlab-org/gitlab-vscode-extension/-/blob/main/package.json
• Add SVG Icon
• Update unit tests

Weight

Weighting a 2 only because it's my first time adding a nav item and to account for the learning curve + unit tests. Also effort to add ICON

Future additions should be easier

Screenshots

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