Use upstream SSV DKG base image

[3alpha]

Summary:

• Use ssvlabs/ssv-dkg as the DKG service base image, pinned by DKG_UPSTREAM_VERSION.
• Remove the Alpine build stage that downloaded and unzipped the DKG binary manually.

Testing:

• docker manifest inspect ssvlabs/ssv-dkg:v3.0.3
• docker build not run locally because the Docker daemon socket is unavailable.

[github-actions]

Dappnode bot has built and pinned the built packages to an IPFS node, for commit: 6d2675d

This is a development version and should only be installed for testing purposes.

1. Package ssv.dnp.dappnode.eth

Install link

Hash: /ipfs/QmZ7XSkq2wo4MDgvvCrqU49xeDcd2zFU795gCsQWZSx7sj

(by dappnodebot/build-action)