go/runtime/scheduling: Consumer should pull from scheduler

[kostko]

Previously the scheduler would push batches to the consumer (e.g. compute
node) which makes no sense as the consumer knows when it's ready to accept
new batches. This changes the model so that the consumer pulls batches from
the scheduler.

[ptrus]

Great! i think this is indeed much better. Thanks for also noticing & fixing the update config stuff.

Looks good, just two minor comments.

[codecov]

Codecov Report

Merging #3569 (7556892) into master (e0f609d) will decrease coverage by 0.08%.
The diff coverage is 71.01%.

@@            Coverage Diff             @@
##           master    #3569      +/-   ##
==========================================
- Coverage   66.64%   66.56%   -0.09%     
==========================================
  Files         377      377              
  Lines       34544    34545       +1     
==========================================
- Hits        23022    22995      -27     
- Misses       8216     8226      +10     
- Partials     3306     3324      +18     

Impacted Files	Coverage Δ
...scheduling/simple/txpool/orderedmap/ordered_map.go	91.07% <50.00%> (+7.28%)	⬆️
go/worker/compute/executor/committee/node.go	65.45% <70.68%> (+0.83%)	⬆️
go/runtime/scheduling/simple/simple.go	81.39% <77.77%> (+2.70%)	⬆️
go/common/sgx/aesm/aesm.go	62.61% <0.00%> (-6.55%)	⬇️
...nsensus/tendermint/apps/staking/signing_rewards.go	20.00% <0.00%> (-5.72%)	⬇️
go/consensus/tendermint/full/services.go	81.35% <0.00%> (-4.24%)	⬇️
go/storage/mkvs/insert.go	87.67% <0.00%> (-4.11%)	⬇️
go/consensus/tendermint/apps/staking/staking.go	51.70% <0.00%> (-2.73%)	⬇️
go/worker/common/committee/node.go	69.68% <0.00%> (-2.66%)	⬇️
go/consensus/tendermint/roothash/roothash.go	71.23% <0.00%> (-2.47%)	⬇️
... and 20 more

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