Add maven proxy configuration.

[vkryachko]

Fixes #12

[vkryachko]

/retest

[vkryachko]

/retest

[ashwinraghav]

;tldr I think we should ship this, and keep an eye out.

The risks I see are that we have a cache that does not have a strict notion of the fact that it is caching maven artifacts, which might lead to some unexpected caveats in the future.

One area that bjornick@ mentioned that is worth exploring is to mount a shared directory for the maven cache with individual containers each having their own gradle cache. Something worth exploring if this does not work out reasonably.

[vkryachko]

SG

One area that bjornick@ mentioned that is worth exploring is to mount a shared directory for the maven cache with individual containers each having their own gradle cache. Something worth exploring if this does not work out reasonably.

This is exactly the setup we have today and it still causes lock contention because multiple gradle processes try to populate the cache as they run. Also this approach relies on gradle's current cache directory layout which is not documented and afaik is not guaranteed to be stable.