Add a disable GC option to config

[elmattic]

Issue summary

In some cases like testing quickly a new feature or just doing some performance benchmark on mainnet, we would like to disable entirely GC in Forest.
Garbage Collection can add a significant overhead to the application, and you only really need it when running a production node.

Other information and links

https://github.com/ChainSafe/forest/blob/main/forest/shared/src/cli/config.rs#L176

[hanabi1224]

@elmattic How about a command line option --no-gc?

[elmattic]

👍 I'm fine with that. Actually I think it doesn't need to be in config file since it's something more for us.