Reset gauges when collecting service metrics

[cezarygerard]

otherwise deleted services will appear in metrics forever it their label combination was unique

[cezarygerard]

/assign @panslava

[cezarygerard]

/assign @aojea

[cezarygerard]

/assign @mmamczur

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[code-elinka]

@cezarygerard
just a nitpick to replace otherwise deleted services will appear in metrics forever it their label combination was unique with otherwise deleted services will appear in metrics forever IF their label combination was unique.

Looks good to me.

[code-elinka]

/lgtm

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[mmamczur]

weren't we concerned before that this can make the metrics show 0 if collected at a bad moment?