Support multiple accountIds for RaaS support

[samlaf]

This is a feature suggestion coming from us. Hasn't been requested (yet) by any RaaS. Just opening as a tracker and for external visibility.

Right now eigenda-proxy uses a single eigenDAClient, which implies they can only have a single account_id loaded. This means all of the rollups they support are (for v1) being rate limited (and for v2) paying from the same account_id.

Not sure whether supporting multiple account_ids is needed or not, we would need to better understand how RaaSs' setup works. Perhaps we could hold a mapping from ip to account_id which they could load as an initial config?

[samlaf]

One suggestion also to sidestep this issue is to use a separate proxy issue per rollup, which might also be good way deploy this?