Add support custom WAL_LEVEL

[eazytry]

Hello!
I was tryed to set 'logical' wal level and it's very difficult.
So i found out the solution by only using migration tools, but i think it could be better to have a way to change any postgres parameters from envs or smth like that.

For example:
create env variable for postgres params like 'PGS_PARAMS' and set it manually, then apply params near post_init step.