Add a proposer config file to our release testing nodes

[mehdi-aouadi]

We'd want at least one of our nodes to be using a proposer config file in order to make sure that it loads it correctly and is working as expected when a new teku version is released.

[tbenr]

Fixed here: https://github.com/Consensys/protocols-azure-inventories/commit/9c8c3ac96aee13b99835f240165445658261f0ff