registry: Add runtime-specific staking thresholds

[kostko]

TODO

• Tests (also improves existing registry tests).

[codecov]

Codecov Report

Merging #2995 into master will decrease coverage by 0.02%.
The diff coverage is 82.45%.

@@            Coverage Diff             @@
##           master    #2995      +/-   ##
==========================================
- Coverage   68.45%   68.42%   -0.03%     
==========================================
  Files         365      365              
  Lines       35679    35834     +155     
==========================================
+ Hits        24423    24521      +98     
- Misses       8111     8155      +44     
- Partials     3145     3158      +13     

Impacted Files	Coverage Δ
go/common/quantity/quantity.go	88.07% <0.00%> (-4.24%)	⬇️
...ensus/tendermint/apps/staking/state/accumulator.go	67.16% <ø> (ø)
go/oasis-node/cmd/registry/runtime/runtime.go	58.75% <55.55%> (-0.31%)	⬇️
go/registry/api/api.go	40.51% <71.42%> (+1.19%)	⬆️
...consensus/tendermint/apps/registry/transactions.go	54.08% <75.00%> (+4.08%)	⬆️
go/registry/api/runtime.go	49.47% <75.00%> (+5.16%)	⬆️
go/staking/api/api.go	74.11% <81.08%> (+2.68%)	⬆️
go/registry/api/sanity_check.go	59.11% <88.88%> (+1.12%)	⬆️
go/registry/tests/tester.go	91.59% <100.00%> (+0.32%)	⬆️
go/upgrade/migrations/dummy.go	80.00% <100.00%> (ø)
... and 33 more

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 10f076d...c4d3bdd. Read the comment docs.