chore: refactor gmp express example

[npty]

Description

This PR modifies the Call Contract with Token (Express) example. It now aligns with our updated express flow, which no longer requires the GMP Express Service. The example also shows how we compute the express fee.

For testnet runs, the script interacts with the contract at 0x22a214c3c2C23a370414e2A4b2CF829A76c29A1b. It supports both Polygon and Avalanche— our default networks for examples. Users can directly run the example without deploying, this is due to whitelisting limitation.

https://axelarnetwork.atlassian.net/browse/AXE-1303

[StephenFluin]

Users can directly run the example without deploying, this is due to whitelisting limitation.

They can run the example, or can't run the example? How do they get on the allow list?

[npty]

Users can directly run the example without deploying, this is due to whitelisting limitation.

They can run the example, or can't run the example? How do they get on the allow list?

They need to ask us to whitelist their contract address. That's probably too much for user if they just want to try executing it to see how it works.

So, we just deployed the contracts and whitelisted them, and they can just execute the example without deploying it.