Update GetGasPrice RPC endpoint with global MinGasPrice

[crypto-facs]

Description

This PR aims to update GetGasPrice API with the new GlobalMinGasPrice module param. The idea is to return this value as minimum for transactions to adjust to the new decorator.

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[loredanacirstea]

utACK

[fedekunze]

LGTM! Can you update the changelog too? 🙏