types/rest: convenience functions for error checking

[alessio]

Closes: #XXX

Description

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For contributor use:

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[codecov]

Codecov Report

Merging #5900 into master will increase coverage by 0.05%.
The diff coverage is 53.84%.

@@            Coverage Diff             @@
##           master    #5900      +/-   ##
==========================================
+ Coverage   56.99%   57.04%   +0.05%     
==========================================
  Files         342      342              
  Lines       20060    20056       -4     
==========================================
+ Hits        11433    11441       +8     
+ Misses       7782     7770      -12     
  Partials      845      845              

[jgimeno]

A way to make people use this can be to update the scaffold tool here:

https://github.com/cosmos/scaffold/blob/master/templates/module/client/rest/query.go.tmpl
and
https://github.com/cosmos/scaffold/blob/master/templates/module/client/rest/tx.go.tmpl

if not I think will be difficult for people to discover this function exists.

[alexanderbez]

LGTM

[alexanderbez]

@jgimeno keep in mind, a large part of that REST boostrapping logic will change with gRPC/Proto. See ADR 021.