Add pprof endpoint to docker-driver.

[cyriltovena]

Signed-off-by: Cyril Tovena cyril.tovena@gmail.com

This will help #3319 understand what's going on.

[codecov-io]

Codecov Report

Merging #3331 (a79b322) into master (8a9b94a) will decrease coverage by 0.06%.
The diff coverage is 0.00%.

@@            Coverage Diff             @@
##           master    #3331      +/-   ##
==========================================
- Coverage   62.78%   62.71%   -0.07%     
==========================================
  Files         204      204              
  Lines       17266    17272       +6     
==========================================
- Hits        10840    10832       -8     
- Misses       5455     5468      +13     
- Partials      971      972       +1     

Impacted Files	Coverage Δ
cmd/docker-driver/main.go	0.00% <0.00%> (ø)
pkg/querier/queryrange/limits.go	91.66% <0.00%> (-4.17%)	⬇️
pkg/promtail/targets/file/filetarget.go	62.75% <0.00%> (-2.07%)	⬇️
pkg/ingester/checkpoint.go	72.62% <0.00%> (-1.15%)	⬇️
pkg/logql/evaluator.go	89.83% <0.00%> (-0.36%)	⬇️
pkg/querier/queryrange/downstreamer.go	97.64% <0.00%> (+2.35%)	⬆️