make coveralls upload/reporting optional in all workflows #717

Job	Run time
Build and push main snapshot images (s390x, linux)	22m 12s
Build and push main snapshot images (ppc64le, linux)	22m 16s
Build and push main snapshot images (arm64, linux)	23m 56s
build-coverage	4m 44s
Build and push main snapshot images (amd64, linux)	2m 11s
build-multiarch / create and push a multiarch manifest to the repo	14s
	1h 15m 33s

Provide feedback