Since:
* We want the S3 bucket to be owned by a different AWS account and it's
not possible to transfer ownership of an existing bucket.
* In the future we want to rebuild some of the Python runtime archives
(for example to improve the sqlite3 handling, or to tweak the compile
flags used), and it will be easier to reason about the change if we
can guarantee only recent buildpack versions are using the assets
rather than several year old unmaintained forks.
The assets were synced from the old bucket using (minus the `--dryrun`):
```
aws s3 sync s3://lang-python s3://heroku-buildpack-python \
--dryrun \
--metadata-directive REPLACE \
--exclude "*" \
--include 'common/*' \
--include 'heroku-*/runtimes/*' \
--include 'heroku-*/libraries/vendor/gdal.tar.gz' \
--include 'heroku-*/libraries/vendor/geos.tar.gz' \
--include 'heroku-*/libraries/vendor/proj.tar.gz' \
--exclude 'common/pip-20.0.2-py2.py3-none-any.whl' \
--exclude '*/runtimes/*-opt.tar.gz' \
--exclude '*/runtimes/sqlite-free/*'
```
The files that were `--exclude`d are those that are no longer used,
or test assets that were not officially released.
The Cedar-14 assets were not migrated since it's EOL next month.
The old S3 bucket will be left untouched for the foreseeable future
(ie: we won't be deleting it), since builds using older versions of this
buildpack (either due to pinning to a tag or via a fork) will still be
using assets from it.
Closes @W-8060097@.
* Switches from using Python 2 to Python 3 for `bob-builder`
* Adds `--no-install-recommends` to reduce unnecessary packages
* Removes unnecessary pinning of pip for Heroku-18 build
* Moves `DEBIAN_FRONTEND` to RUN level env var, given:
https://serverfault.com/a/797318
Refs @W-8119717@.
[skip changelog]
Ed Morley