Problem description

Include configs to easily connect to the ephemeral testnet, "ephemery".

Description of Ephemery, its behaviour and the integration plans by @taxmeifyoucan :
Ephemery is a new kind of testnet which is intended for short term testing use cases. It automatically resets back to genesis after every given period which enables reclaiming faucet funds, clearing validator set and keeping small state.

Ephemery runs since December 2022 but is mostly run by external tooling. There is ongoing effort to implement specs also within clients, not only externally. All resources for using the testnet are here: https://github.com/ephemery-testnet/ephemery-resources.

Current specs for client requirements can be found in the draft EIP.

Solution description

Add the --ephemery config.
Add additional flags for developer options related to downloading / generating genesis (see below).

Additional context

Add Ephemery to the Lodestar network options (cli and config packages)

• Add ephemery flag

Additional genesis options
Default: load genesis from a URL (checkpointz server). Additional [developer] options currently envisaged:

• Use backup download URL (ephemery.dev)
• Use flag to override with custom path to a genesis.ssz file provided by user
• Use flag to generate genesis with script at packages/ephemery. Note: user dependency eth2-testnet-genesis.

Reset

• Research phase ongoing for ephemery reset.