Add support for curly brackets when resolving envs

[kkawula]

Which components does the task require to be changed? (think hard pls)

snforge

Description

Currently forge support such syntax: url = "$RPC_URL", but url = "${RPC_URL}" should be possible

Make it possible: https://t.me/starknet_foundry_support/5363

[emarc99]

I can handle this if assigned. I will study the codebase, check relevant crates, implement the feature and ensure test pass. Like I did here.