Failed task signature on error handler

[nicklaros]

Current error handler only accept error as arguments, I propose to add failed task signature to make it more useful. Some use case is when we need to broadcast error event about failed task to notify other system.

[codecov[bot]]

Codecov Report

Merging #615 into master will increase coverage by 0.03%. The diff coverage is 0.00%.

@@            Coverage Diff             @@
##           master     #615      +/-   ##
==========================================
+ Coverage   37.24%   37.27%   +0.03%     
==========================================
  Files          36       36              
  Lines        3112     3109       -3     
==========================================
  Hits         1159     1159              
+ Misses       1805     1802       -3     
  Partials      148      148              

Impacted Files	Coverage Δ
v2/worker.go	2.25% <0.00%> (+0.03%)	:arrow_up:

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