Add insufficient_fees ocurrences to prometheus metrics

[sryps]

Summary

As operators managing gas-prices and fee related parts of relaying we try to keep gas-prices at a reasonable point to successfully relay packets without "over-paying" for fees.

If we could monitor if insufficient fees was happening it would make it easier for us to find the floor of what our gas-price could be.
Maybe this could actually be a bigger task where it actually reports what we are paying in fees and whether the gas-price could be reduced?

https://www.mintscan.io/osmosis/tx/71462314D245909C10BE1A6A0B0DA184B50A3C756F48A7229920A224B41EEC28?height=12502246
https://www.mintscan.io/osmosis/tx/1FA640B1B16A0A5B9246572C0DBF9D50CC772EA6EFEBA6FF25B7F477D1B810C1?height=12502247

These 2 TXs are a perfect example of having a similar tx, similar gas but clearly one relayer has gas-price set much higher and paying almost 12 times more in fees!

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