Enable CLI parameter specification via env vars

[FabijanC]

Usage related changes

• Closes #482
• Closes #475
• More info in the updated .md documentation files
• Improves #[arg(value_name = ...)] of some CLI parameters.

Development related changes

• Enable the env feature of the clap dependency in Cargo.toml.
• Introduces serial_test dev dependency because env-mainpulating tests cannot be run in parallel.
  • Apparently env::remove_var should be unsafe but isn't.

Checklist:

• [x] Checked out the contribution guidelines
• [x] Applied formatting - ./scripts/format.sh
• [x] No linter errors - ./scripts/clippy_check.sh
• [x] No unused dependencies - ./scripts/check_unused_deps.sh
• [x] No spelling errors - ./scripts/check_spelling.sh
• [x] Performed code self-review
• [x] Rebased to the latest commit of the target branch (or merged it into my branch)
• [x] Updated the docs if needed - ./website/README.md
• [x] Linked the issues resolvable by this PR - linking info
• [x] Updated the tests if needed; all passing - execution info

[FabijanC]

What will happen if cli args and env variables are passed

I thought I added this info, thanks for reminding me. Updated the docs in https://github.com/0xSpaceShard/starknet-devnet-rs/pull/483/commits/e268e43c7bfbacee77f9040e1cc1c75ede011f5a