Eth2.0: Prevent from running more than 1 validator

[pablomendezroyo]

Context

Due to the upcoming Ethereum consensus multiclient support on DAppNode there must be some restrictions to do not allow to run more than 1 Ethereum consensus validator at the same time, otherwise, it could lead to slashing.

Restrictions to avoid running two Eth2.0 validators at the same time

• Add the same bind port to the validator docker-compose.yml: this would prevent from running the same docker container on the host due to Docker internal restrictions (It will throw the error Bind for 0.0.0.0:XXXX failed: port is already allocated)
• Use docker tagging method for Eth2 packages and have a better track of them
• Allow installing and syncing the beacon chain of any other Eth2.0 client: this would prepare everything before switching the Eth2.0 validator
• Add a restart policy of never when switching Eth2 client
• Use of slashing protection data OR add a delay of 20 minutes before switching the consensus validator: this restriction should be enough to avoid slashing and penalties.

Depends on dappnode/DAppNode#329

[pablomendezroyo]

Already handled with web3signer and global envs to only listen requests from selected clients