Switch MAINTAINER to LABEL directive in Docker

[Mr0grog]

We use the MAINTAINER directive in our docker files, but it’s been deprecated:

The LABEL instruction is a much more flexible version of this and you should use it instead, as it enables setting any metadata you require, and can be viewed easily, for example with docker inspect. To set a label corresponding to the MAINTAINER field you could use:

LABEL maintainer="SvenDowideit@home.org.au"

• MAINTAINER docs
• LABEL docs