add ARM64 Arch

[alexpeterson91]

Nimbus claims to be great on small and embedded systems, should make it availible for pi users

[pablomendezroyo]

When the eth2 multiclient project started, I quit from working with ARM since it was slaying down my progress. I think now we can retake it and start implementing ARM everywhere: execution, consensus, signer and mevboost

[alexpeterson91]

@Nabsku and I have Besu tested and ready for mainnet and goerli/prater in both architectures. I'll spend some time next week seeing what other packages can be done just adding the arch to the manifests and see what needs to be added to make the ARM64 work. Obviously we won't need to make all clients work but the more diversity the better. I also feel like the newest Pi4 8GB RAM is still gonna be pretty limiting in the post merge ecosystem, so definitely should focus first on the clients designed for small and embedded systems like Nimbus.

I guess I also am wondering if Nimbus EL is far enough along to test on goerli. I know it's still in the experimental phase but I feel like it's been in that spot for a while now. Regardless I'd like to see how it works even not on dappnode, it's the last client aside from lodestar (which I want an update on @dapplion lol) I haven't used ever yet.