Add MongoDB and "info" and helm3 for metrics-server

Changelog for 0.7.9:

• PR #165 Add app for MongoDB (review / rebase from Prateek's PR) by @alexellis

• PR #164 apps: add crossplane by @hasheddan

• PR #162 Fix Travis badge by @braybaut

• Add "info" and helm3 for metrics-server

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