docs: add auth/gasprice query documentation and gas price mechanism explanation

[Davphla]

fix: #4529
fix: #4997

queryGasPrice function can be found in tm2/pkg/sdk/auth/handler.go:L83.

Reference: #2838

[Gno2D2]

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[Davphla]

Would be a good idea to calculate that rate automatically when calling auth/gasprice

[MikaelVallenet]

In the Gas Price section would be nice to maybe explain what happens in case of error (e.g gas too low and give an example) it could help newcomers facing gas issues to identify the solution faster wdyt ?

[MikaelVallenet]

do we have a doc or link to explain more about this (how a validator can set minimum ...blabla)
if not it's fine but feel like it can be good here since it's a small note and people may be interested to learn more about validators config when reading this.

[Davphla]

Fix: 1dff049
The documentation does not exist on the mono-repo.
There's existing explanation on https://gnops.io/articles/guides/local-chain/#1-generate-the-node-directory-secrets--config, but it is explained implicitly.

[MikaelVallenet]

LGTM overall, i let some comment that would be improvements IMO

[Villaquiranm]

Nice doc :) LGTM

[jefft0]

MikaelVallenet approved. Ready for core dev review.