MEV_RELAYS can now be multi-line

[yorickdowne]

This is a fairly big change to enable one thing: Multi-line values in .env. There is one user that has their MEV_RELAYS as multi-line, and we kept breaking their .env whenever the version of the template changed.

Not touching the config workflow deeply, but that could be next - it'd make a lot of sense to re-use the Lido CSM config flow for all MEV_RELAYS purposes, or at least when MEV_RELAYS has not been set by the user, and construct multi-line during config.

That'd be a separate PR

[yorickdowne]

I am merging this without review, so I can increment the .env version for the ssvlabs repo changeover. Without this, I'll break the setup of the one user that has a multi-line value :/

The awk code is GPT-generated. A review is still welcome, we may want to tighten / improve it