docs: update the nonces docs in QGB store

[rach-id]

Overview

Closes #1805

The latest attestation nonce and earliest attestation nonce are values written to store. In order to get them, we use the getLatestAttestationNonce and the getEarliestAvailableAttestationNonce methods.

These methods panic if these values don't exist in store. However, the only time these values don't exist in store, if no manual changes were done to the store, is during the period between chain startup and block 1.

So, we have the CheckLatestAttestationNonce method that checks if the value exists in store and returns true if so. And we use it in abci.EndBlocker and in queries not to return a stack trace, but a relevant error when querying during the period between chain startup and block 1.

Thus, the only change we can do is think about in this case, is having these methods return an error instead of panicking, but it returns the same thing via using the CheckLatestAttestationNonce, instead of using if errors.Is(...).

This is why this PR removes the misleading docs but makes no changes on the methods.

[codecov-commenter]

Codecov Report

Merging #1841 (98c470f) into main (1b33d58) will increase coverage by 0.03%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##             main    #1841      +/-   ##
==========================================
+ Coverage   21.79%   21.82%   +0.03%     
==========================================
  Files         116      116              
  Lines       13247    13247              
==========================================
+ Hits         2887     2891       +4     
+ Misses      10068    10065       -3     
+ Partials      292      291       -1     

Impacted Files	Coverage Δ
x/qgb/keeper/keeper_attestation.go	66.66% <ø> (ø)

... and 1 file with indirect coverage changes