beacon: Transaction handling fixes

[kostko]

• go/consensus: Add support for method priority

• go/beacon: Make beacon methods critical and ignore tx authentication

  There is no sense in handling transaction authentication and fees for beacon
  methods which can only be invoked by the block proposer.

• e2e/runtime: Also configure intervals for PVSS backend

• go/beacon: Only allow a single beacon transaction per block

[codecov]

Codecov Report

Merging #3675 (46851ca) into master (30110a5) will increase coverage by 0.05%.
The diff coverage is 65.90%.

@@            Coverage Diff             @@
##           master    #3675      +/-   ##
==========================================
+ Coverage   66.64%   66.69%   +0.05%     
==========================================
  Files         393      391       -2     
  Lines       38366    38160     -206     
==========================================
- Hits        25569    25451     -118     
+ Misses       9120     9049      -71     
+ Partials     3677     3660      -17     

Impacted Files	Coverage Δ
go/consensus/tendermint/api/api.go	82.89% <0.00%> (-1.11%)	⬇️
go/oasis-node/cmd/genesis/genesis.go	53.99% <ø> (-0.10%)	⬇️
go/consensus/tendermint/abci/mux.go	57.64% <33.33%> (-1.09%)	⬇️
...o/consensus/tendermint/apps/beacon/backend_pvss.go	59.56% <64.70%> (-0.27%)	⬇️
.../consensus/tendermint/apps/registry/state/state.go	57.05% <71.42%> (+0.53%)	⬆️
go/beacon/api/pvss.go	80.00% <100.00%> (+5.00%)	⬆️
go/consensus/api/transaction/transaction.go	55.91% <100.00%> (+3.04%)	⬆️
go/consensus/api/transaction/results/results.go	0.00% <0.00%> (-100.00%)	⬇️
go/worker/storage/service_external.go	40.74% <0.00%> (-11.12%)	⬇️
go/consensus/tendermint/abci/state/state.go	54.54% <0.00%> (-9.10%)	⬇️
... and 38 more

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