When the AWS Account ID is provided, we must check that it is a valid
one.
AWS Account ID is a well documented field: 12-digit string
This check is meant to prevent typos when creating Databases mainly from
the Web UI in the context of Teleport Discover.
The use of a re-badged buildbox image (rebadging quay.io/gravitational/teleport-buildbox to us-docker.pkg.dev/ci-account/teleport/buildbox-root) is holdover from when CI builds required separate "root user" and "non-root user" images to execute tests under different contexts.
This requirement has since been lifted by using a Go-based build script in CI, and the having to manually invoke a process to re-badge the buildboxes is, tedious, confusing and causing stoppages.
This patch restores the use of buildboxes from quay.io in CI.