use registry input in image tags

[squarebracket]

It seems that the registry input wasn't actually being used anywhere, so I added a line to prepend the registry with a / to each inputs.Tags. This way it should build/push for the given registry.

[jerray]

You can find its usage in entrypoint.sh. It is only used to login to the docker registry.
I think user should provide full repository name including registry path. Repository name should be same as the result of docker image ls command.

[squarebracket]

Hmm. You don't think it's redundant to have the registry both as its own field and in the repository field? Correct me if I'm wrong, but I don't think docker hub allows for several nested levels, so if you prefer to have the registry as part of the repository field (as opposed to completely separate as in this pr), you could simply chop off what's before the first / if there are two or more /s in the repository and use that for the login.

[jerray]

I come up with a solution. When registry is provided, check if repository has prefix same as the registry. If not, prepend registry and / to the repository. You should change inputs.Repository other than inputs.Tags.
By the way, we use tab to indent in Golang. You can use gofmt or goimports to format files automatically.

[squarebracket]

Changed.

I also added a .editorconfig file so that tabs are used instead of spaces.

[jerray]

@squarebracket Thanks. I'll merge this pr later.