Support service bindings in build stages

[braunsonm]

It has become the standard to use service bindings in order to configure buildpacks with custom configuration. For instance, Paketo describes binding configuration in detail here: https://paketo.io/docs/howto/configuration/#bindings

In order to support things like 1) private maven repositories, 2) custom CAs, etc service bindings are required. The pack CLI supports this through --volumes flag allowing of passing through volumes to the build context.

I propose func build support the same thing with a --volumes maven/:/platform/bindings/maven which would allow custom maven settings.xml to be provided for private registry username and passwords in a secure manor.

[swastik959]

/assign