monorepo breaks in-dyno postgres addon, within CI pipeline

[trey-mindtrip]

If you add a postgres addon via your app.json, to be used during your CI testing, and you are using this buildpack, the test setup fails when it tries to find the DB the first time, with an error like "could not open file global/pg_filenode.map". This was observed with a Rails project, but I think the issue is generic, and I suspect in-dyno Redis addons also get messed up.

The problem is when using these in-dyno addons, Heroku adds a couple buildpacks that run before any of the app buildpacks, and they install directories like /app/.indyno, /app/.profile.d and /app/.sprettur (at least those are what I found when debugging). When monorepo comes along to do its thing, it wipes out /app/*, and the addons are broken.

I have a simple fix that is working for me at master...mindtrip-ai:heroku-buildpack-monorepo:master . I was undecided about preserving specific Heroku files, but wound up preserving all dotfiles in case the Heroku set expands.