Create Rust how-tos according to the proposed ISC docs structure

[Jeroen van den Hout]

Provide code examples for the following how-tos from the proposed structure (#1359):

• Test a smart contract
• Deploy a smart contract
• Get Balance
• Create a basic contract
• Withdraw base tokens
• Withdraw native assets
  • NFT
  • Native Token
• Generate Randomness
• Mint a Custom Token
• Mint an NFT