Missing integrity check in Dragonwell Dockerfile

[steelhead31]

Found as part of TrailOfBits Audit:

Ref: TOB-TEMURIN-6

The Dragonwell Dockerfile downloads and installs the Dragonwell software without
verifying its integrity. The integrity should be verified using a hashsum like SHA256 to
ensure the integrity of the download, and ensure that the system is receiving the same
data across multiple downloads.

See ToB report for further details.