feat: add EstimateGas to gnoclient

[zivkovicmilos]

Description

Closes #1826 along with gnolang/tm2-js-client#192

This PR introduces a method EstimateGas to estimate the gas used by a transaction in gnoclient.
We can use this call to get a ballpark estimate if a transaction succeeds, and if it does, how much gas it actually used.

[Gno2D2]

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[codecov]

Codecov Report

Attention: Patch coverage is 75.00000% with 6 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
gno.land/pkg/gnoclient/client_txs.go	75.00%	4 Missing and 2 partials ⚠️

📢 Thoughts on this report? Let us know!

[gfanton]

looks good 👍

[thehowl]

just 2c post merge: shouldn't we expose the Simulate method?

The problem I see with this method is that it still requires for us to encode a transaction where on the user side we put the maximum gas value. Because of that, having a Simulate method, which can be used for other use-cases, seems more appropriate.