Add Error method for step evaluators

[adityacs]

What this PR does / why we need it:
Adds Error method for step evaluators

Which issue(s) this PR fixes:
Fixes #2208

Checklist

• Tests updated

[adityacs]

@cyriltovena Kindly review this. I will add the tests if the changes made are fine.

[codecov-commenter]

Codecov Report

Merging #2223 into master will increase coverage by 0.06%.
The diff coverage is 73.68%.

@@            Coverage Diff             @@
##           master    #2223      +/-   ##
==========================================
+ Coverage   62.14%   62.21%   +0.06%     
==========================================
  Files         154      154              
  Lines       12457    12493      +36     
==========================================
+ Hits         7741     7772      +31     
- Misses       4108     4113       +5     
  Partials      608      608              

Impacted Files	Coverage Δ
pkg/logql/sharding.go	59.79% <50.00%> (-0.65%)	⬇️
pkg/logql/step_evaluator.go	66.66% <66.66%> (-2.57%)	⬇️
pkg/logql/evaluator.go	92.10% <84.61%> (-0.62%)	⬇️
pkg/logql/engine.go	91.39% <100.00%> (+1.39%)	⬆️
pkg/logql/matrix.go	100.00% <100.00%> (ø)
pkg/logql/range_vector.go	97.70% <100.00%> (+0.05%)	⬆️
pkg/logql/series_extractor.go	94.59% <100.00%> (+0.30%)	⬆️
pkg/querier/queryrange/downstreamer.go	95.87% <0.00%> (-2.07%)	⬇️
... and 2 more

[cyriltovena]

Yep looks good ! I need just one single test for this. Basically a regression test, something that create an engine with a fake querier.

The querier iterator should return an error and verify that the engine exec also return an error, no need to be fancier than that.

[cyriltovena]

Awesome work ! Thank you !