Add basic logging

Log environment variables and configuration files (as they are read)
to a file in the application directory named:

buildpack-diagnostics/buildpack.log

Also log exceptions caught in the detect, compile, and release
scripts to the above file.

Log the full path of buildpack.log, which captures the application
directory too.

[#51900805]
Merge 51900805- to master

[Completes #51900805]