IE-4281 Modernize and simplify

[djeebus]

This does a lot, but mostly removes unused code (as evidenced by the removal of the 162 KLOC:

• remove weave/cloud specific tooling
• upgrade to golang 1.19
• use go.mod
• use github CI
• deploy images to ghcr
• fix a small bug that renders superfluous text when storing summaries

[mplachter]

LGTM 🚀