Fix ENSAdmin Docker image variable passing

[BanaSeba]

NEXT_PUBLIC_SERVER_CONNECTION_LIBRARY is not visible in the ENSAdmin app while running outside of Vercel.
We need to adjust the app logic for this to work.

[lightwalker-eth]

A temporary solution to this issue was achieved through #1039

Current idea for solving this is that we may be switching ENSAdmin away from using Next.js and turning it into a purely frontend React app.

We are in the middle of other priority refactorings of ENSAdmin right now. Therefore this issue is in our backlog for now.

[lightwalker-eth]

This issue is planned to be solved through changing ENSAdmin away from Next.js