chore: use fedimint's overlay

[dpc]

@justinmoon

[justinmoon]

@dpc we still need to backport this. 0.2 branch is where the flake is broken on MacOS. This PR was attempting to fix it: https://github.com/fedimint/ui/pull/377

Some issues with the backport in fedimint https://github.com/fedimint/fedimint/pull/4349

[justinmoon]

I still can't run nix develop on master (8713bb828f050f18c386abd200e5b17ef7a8d844):

$ nix develop
error: builder for '/nix/store/0f3p440vzing4xpdf9j37kq34z110hjz-bitcoind-26.0.drv' failed with exit code 2;
       last 10 log lines:
       > ./support/allocators/pool.h:250:15: error: aligned deallocation function of type 'void (void *, std::align_val_t) noexcept' is only available on macOS 10.14 or newer
       >             ::operator delete (p, std::align_val_t{alignment});
       >               ^
       > ./support/allocators/pool.h:250:15: note: if you supply your own aligned allocation functions, use -faligned-allocation to silence this diagnostic
       > 4 errors generated.
       > make[2]: *** [Makefile:10024: libbitcoin_node_a-blockencodings.o] Error 1
       > make[2]: Leaving directory '/private/tmp/nix-build-bitcoind-26.0.drv-0/bitcoin-26.0/src'
       > make[1]: *** [Makefile:20138: all-recursive] Error 1
       > make[1]: Leaving directory '/private/tmp/nix-build-bitcoind-26.0.drv-0/bitcoin-26.0/src'
       > make: *** [Makefile:814: all-recursive] Error 1
       For full logs, run 'nix log /nix/store/0f3p440vzing4xpdf9j37kq34z110hjz-bitcoind-26.0.drv'.
error: 1 dependencies of derivation '/nix/store/y5pxhj8q1536kihb72ms39n7cfx0n9f5-nix-shell-env.drv' failed to build

[Kodylow]

I was able to build with this commit : a9e807e4e0325ce8d93d4af212309a183e87d89a