This script sets up the tuf-on-ci repository so that the initial
signing event can be run.

Signed-off-by: Jussi Kukkonen <jkukkonen@google.com>

These are likely not complete (e.g. key generation is under-documented).

Signed-off-by: Jussi Kukkonen <jkukkonen@google.com>

import-config.json is used as argument to tuf-on-ci-import-repo, it
includes:
* offline role expiry and signing periods to set in metadata
* keyowners or online signing key identifiers for existing keys
* snapshot key is left with placeholder value: it (along with online
  expiry and signing periods) is expected to be modified with a
  tuf-on-ci-delegate call in the same signing event

Signed-off-by: Jussi Kukkonen <jkukkonen@google.com>

Signed-off-by: Jussi Kukkonen <jkukkonen@google.com>