Added docker login step to Megalinter github action#366

KieranWardle wants to merge 1 commit intomainONSdigital/ssdc-rm-support-tool:mainfrom

SDCSRM-729_Megalinter-docker-loginONSdigital/ssdc-rm-support-tool:SDCSRM-729_Megalinter-docker-loginCopy head branch name to clipboard