[WIP] feat: flush metrics on shutdown #758

Job	Run time
Build Prometheus for common architectures	0s
Build Prometheus for all architectures (0)	8m 40s
Build Prometheus for all architectures (1)	12m 15s
Build Prometheus for all architectures (2)	8m 22s
Build Prometheus for all architectures (3)	12m 24s
Build Prometheus for all architectures (4)	8m 31s
golangci-lint	3m 12s
Go tests	22m 48s
Build Prometheus for all architectures (5)	11m 45s
Build Prometheus for all architectures (6)	10m 29s
Mixins tests	2m 7s
Build Prometheus for all architectures (7)	12m 39s
UI tests	2m 16s
Build Prometheus for all architectures (8)	8m 16s
Build Prometheus for all architectures (9)	12m 39s
Go tests on Windows	9m 41s
Build Prometheus for all architectures (10)	8m 18s
Build Prometheus for all architectures (11)	12m 12s
codeql / Analyze (go)	18m 40s
fuzzing / Fuzzing	0s
codeql / Analyze (javascript)	1m 34s
Publish UI on npm Registry	0s
Publish main branch artifacts	0s
Publish release artefacts	0s
	3h 6m 48s

Provide feedback