mgr/dashboard: bump ng2-charts in /src/pybind/mgr/dashboard/frontend

Bumps [ng2-charts](https://github.com/valor-software/ng2-charts) from 4.1.1 to 6.0.0.
- [Release notes](https://github.com/valor-software/ng2-charts/releases)
- [Commits](valor-software/ng2-charts@v4.1.1...v6.0.0)

---
updated-dependencies:
- dependency-name: ng2-charts
  dependency-type: direct:production
  update-type: version-update:semver-major
...

Signed-off-by: dependabot[bot] <support@github.com>

src/pybind/mgr/dashboard/frontend/package.json

@@ -71,7 +71,7 @@
     "moment": "2.29.4",
     "ng-block-ui": "3.0.2",
     "ng-click-outside": "7.0.0",
-    "ng2-charts": "4.1.1",
+    "ng2-charts": "6.0.0",
     "ngx-pipe-function": "1.0.0",
     "ngx-toastr": "17.0.2",
     "rxjs": "6.6.3",