Add arm64, ppc64el and s390x and migrate workflows to charm-ci #424

Job	Run time
integration-test / Test matrix	1m 1s
integration-test / build / Build matrix	32s
integration-test / build / Build charm aproxy (arm64)	2m 41s
integration-test / build / Build charm aproxy (amd64)	2m 45s
integration-test / build / Build charm aproxy (ppc64el)	2m 46s
integration-test / build / Build charm aproxy (s390x)	2m 26s
integration-test / matrix.name	0s
integration-test / build / Collect artifacts	1s
Required Integration Test Status Checks	1s
	12m 13s

Provide feedback