KB article on using the Apt Buildpack

[mheadd]

For applications using that rely on components installed using the apt buildpack, some additional steps might be required to ensure successful installation of software packages. Details captured here: https://gsa-tts.slack.com/archives/C09CR1Q9Z/p1634070240002900

We should write this up as a knowledge bae article for other platform users that rely on the apt buildpack.

[mogul]

Here's the key .profile content that was needed to fix up the naive installation of default-jre-headless post-installation.

[mogul]

(Note it may be the simplest increment to just write up how to use java in particular, since other packages may not need this kind of wrangling and installing java is likely the most common reason people resort to apt-buildpack.)