add cosmos GMP address to reference page

[StephenFluin]

axelar1dv4u5k73pzqrxlzujxg3qp8kvc3pje7jtdvu72npnt5zhq05ejcsn5qme5

Consider making it a global variable that is imported, as it's also here: https://docs.axelar.dev/dev/send-tokens/overview#sendtoken-from-a-cosmos-based-source-chain

[ffe9f8]

Have variable across entire doc set so that we can share a common value