cos-dkms: Release cos-dkms v0.2.0

This adds the --insert-on-install flag and allows the reading of
environment variables from an lsb-release file. Additionally, this fixes
an issue with downloading from GCS buckets whose names have trailing
slashes.

BUG=b/389772265
TEST=cloudbuild and pre-release test
RELEASE_NOTE=Add --insert-on-install flag and improved default value handling to cos-dkms.

Change-Id: I47bd59391422729f0c74e85144570af6d5cd1756
Reviewed-on: https://cos-review.googlesource.com/c/cos/tools/+/90822
Cloud-Build: GCB Service account <228075978874@cloudbuild.gserviceaccount.com>
Reviewed-by: Arnav Kansal <rnv@google.com>
Tested-by: Kevin Berry <kpberry@google.com>