Add the possibility to download schema metadata

[ImFlog]

Fixes #122

Add the ability to download schema metadata using a flag.

[ImFlog]

@ferozed, can you tell me if this implementation would work for you ?

[ferozed]

Looks good. So it will download into the same output folder as normal schema?

Is there a way for me to test this?

[ImFlog]

Yes you can test this, you need to follow the instructions in the readme but a TLDR is to use the publishToMavenLocal task on gradle and than reference the plugin with the mavenLocal in the buildscript repository (like in the examples).

For the other output directory I think we could add the directory in a complex object in the download task extension by I wanted to code something as a POC. I am worried that It could be a problem for json schema (same extension etc).
I can add this capacity next week probably (won't have any more time before the end of the week unfortunately).

[ImFlog]

@ferozed I added the option to specify the metadata directory.
Glad to get feedback on the DSL / usage :)