Add configurable preset using flags

[chetanyb]

Closes #215

Usage

zig build -Dpreset=mainnet

zig build -Dpreset=minimal

[GrapeBaBa]

Is it preset a compile time arg or not in the beacon chain?

[chetanyb]

Is it preset a compile time arg or not in the beacon chain?

yes, it's a compile-time argument.

[chetanyb]

@GrapeBaBa @g11tech

[GrapeBaBa]

Is it preset a compile time arg or not in the beacon chain?

yes, it's a compile-time argument.

Any evidence for it? such as any beacon client cmd flag?

[chetanyb]

Is it preset a compile time arg or not in the beacon chain?

yes, it's a compile-time argument.

Any evidence for it? such as any beacon client cmd flag?

If you meant how other beacon clients do it, the consensus specs state that presets are generally only applicable during compile-time and implementation may choose to only support 1 preset per build-target (https://github.com/ethereum/consensus-specs/tree/dev/presets).

Different clients handle this differently:

• Prysm: Single preset per binary - bazel build --config=minimal (https://github.com/prysmaticlabs/prysm/blob/develop/INTEROP.md)
• Lighthouse: Multiple presets in one binary via trait generics - FEATURES=spec-minimal,gnosis make (https://github.com/sigp/lighthouse/blob/stable/consensus/types/src/eth_spec.rs)
• Nimbus: Single preset per binary
• Lodestar: Runtime selection - --network minimal (https://chainsafe.github.io/lodestar/run/beacon-management/beacon-cli/)