Make `hardhat_reset` more powerful

[fvictorio]

Ideally hardhat_reset would let you change anything that you can configure in the config of the Hardhat network. Right now only the forking part of it can be changed.

I'm not sure if this can be done in a backward-compatible way. At the very least, I made the huge mistake of using different names in the config and in the reset method. But maybe we can add the names in the config to the RPC method and accept both.

Update: any work on this should also include adding a proper network helper in the hardhat-network-helpers package