Fix: admin summary cannot be cached in redis

[topjohncian]

Summary in admin dashboard caching was introduced in 0c9383.
It calls cache.Set function but doesn't handle errors.

If the user enables Redis, it won't successfully set cache because the type of the value cannot be serialized using gob, which is map[string]interface{}

So, we registered the types and fixed that.

[codecov]

Codecov Report

Merging #1329 (1e8b991) into master (21d2b81) will increase coverage by 0.03%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #1329      +/-   ##
==========================================
+ Coverage   89.30%   89.33%   +0.03%     
==========================================
  Files          95       95              
  Lines        8272     8272              
==========================================
+ Hits         7387     7390       +3     
+ Misses        724      721       -3     
  Partials      161      161              

Impacted Files	Coverage Δ
pkg/cluster/pool.go	85.34% <0.00%> (-9.49%)	⬇️
pkg/mq/mq.go	94.11% <0.00%> (-1.48%)	⬇️
pkg/task/pool.go	100.00% <0.00%> (+48.38%)	⬆️

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[HFO4]

Thanks!