add Gradle and Maven into Java8 + bump aws-lambda-builders

[sriram-mv]

👍

[jfuss]

@mhart Would you prefer the gradle and maven to be its own layer (a different RUN command) instead of lumping everything into one? This might be helpful when gradle or maven needs updates but not the runtime itself.

[mhart]

Nah, not too fussed about that – maven and gradle are updated pretty rarely – probably more rarely than the Lambda base OS layer itself is updated – and when that happens we have to rebuild all layers anyway.

[mhart]

Great! Merging now, will let you know when they've all been pushed

[mhart]

All pushed!