feat(CHAIN-4644): add Sepolia FeeDisburser upgrade task

[0xth4nh]

Summary

Adds the Base Sepolia onchain task for CHAIN-4644.

• deploys FeeDisburser version 1.1.0
• upgrades the L2 proxy through OptimismPortal2
• calls initialize([], []) atomically with upgradeToAndCall
• keeps the initial L2 system-address refund configuration empty
• moves active EVM task-specific make targets into each task's task.mk

Validation

• forge clean && forge build
• simulated the L1 Safe payload against Sepolia with the currently deployed implementation address
• verified the live proxy admin, implementation, L1 wallet, and disbursement interval on Base Sepolia

Before signing

• deploy the new implementation
• set FEE_DISBURSER_IMPL_ADDR
• generate base-signer.json
• set skipTaskOriginValidation to true

Depends on #755.

[linear]

CHAIN-4644