CCIP v1.2 upgrade

[andrejrakic]

Upgraded the starter kit to support the v1.2 release of Chainlink CCIP. Notable changes:

• New CCIP Router addresses
• Bumped the @chainlink/contracts-ccip package from v0.7.6 to v1.2.0
• Removed the strict sequencing flag from the extraArgs field in CCIP messages
• Support for Arbitrum Sepolia (instead of Arbitrum Goerli), BNB Chain Testnet, and Base Goerli test networks
• Support for USDC transfers. USDC transfers are currently supported on the following lanes:
  • From Optimism Goerli to Avalanche Fuji.
  • From Optimism Goerli to Base Goerli.
  • From Avalanche Fuji to Optimism Goerli.
  • From Avalanche Fuji to Base Goerli.
  • From Base Goerli to Optimism Goerli.
  • From Base Goerli to Avalanche Fuji.