feature: builder session manager env var config

[allnil]

draft, work on envs

[allnil]

hi ferranbt !
I moved PR and got rid of Viper!
Maybe you could share some nits on how to make it better
thanks :)

[allnil]

hmmm
@ferranbt
There are some issues with example tests
I tried to run them from the main branch and got the same error as in ci log

_2024/03/02 15:58:21 Test address 1: 0x99A24Fe271a0f754fD55A48Cb3b2bC84f16875f7
panic: Post "http://localhost:8555": read tcp [::1]:36920->[::1]:8555: read: connection reset by peer

goroutine 1 [running]:
main.maybe(...)
	/home/runner/work/suave-execution-geth/suave-execution-geth/suapp-examples/examples/build-eth-block/main.go:87
main.main()
	/home/runner/work/suave-execution-geth/suave-execution-geth/suapp-examples/examples/build-eth-block/main.go:24 +0x[91](https://github.com/flashbots/suave-execution-geth/actions/runs/8101826092/job/22204681002?pr=19#step:8:92)1
exit status 2_
make: *** [Makefile:31: run-integration] Error 1