Endorse htlc and local reputation

[thomash-acinq]

We do not yet drop HTLCs, the purpose is to collect data first.

We add

1. An endorsement bit to UpdateAddHtlc. This follows draft: HTLC Endorsement to Mitigate Channel Jamming lightning/bolts#1071.
2. A local reputation system: For each pair (origin node, endorsement value), we compute its reputation as total fees that were paid divided by total fees that would have been paid if all HTLCs had fulfilled. When considering an HTLC to relay, we only forward it if the reputation of its source is higher than the occupancy of the outgoing channel.
3. A limit on the number of small HTLCs per channel. We allow just very small HTLCs per channel so that it's not possible to block large HTLCs using only small HTLCs (similar to Add a channel congestion control mechanism #2330 but continuous).

[codecov-commenter]

Codecov Report

Merging #2716 (deab085) into master (12adf87) will increase coverage by 0.04%.
Report is 1 commits behind head on master.
The diff coverage is 100.00%.

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@@            Coverage Diff             @@
##           master    #2716      +/-   ##
==========================================
+ Coverage   85.82%   85.86%   +0.04%     
==========================================
  Files         216      218       +2     
  Lines       18126    18209      +83     
  Branches      771      749      -22     
==========================================
+ Hits        15556    15636      +80     
- Misses       2570     2573       +3     

Files	Coverage Δ
...re/src/main/scala/fr/acinq/eclair/NodeParams.scala	93.47% <100.00%> (+0.08%)	⬆️
...ir-core/src/main/scala/fr/acinq/eclair/Setup.scala	75.29% <100.00%> (+0.14%)	⬆️
...in/scala/fr/acinq/eclair/channel/ChannelData.scala	100.00% <ø> (ø)
...in/scala/fr/acinq/eclair/channel/Commitments.scala	96.93% <100.00%> (+0.11%)	⬆️
...ain/scala/fr/acinq/eclair/channel/Monitoring.scala	96.15% <100.00%> (+0.23%)	⬆️
...in/scala/fr/acinq/eclair/channel/fsm/Channel.scala	85.80% <100.00%> (+0.15%)	⬆️
...ain/scala/fr/acinq/eclair/payment/Monitoring.scala	98.30% <100.00%> (+0.09%)	⬆️
.../scala/fr/acinq/eclair/payment/PaymentPacket.scala	90.82% <100.00%> (ø)
...a/fr/acinq/eclair/payment/relay/ChannelRelay.scala	96.03% <100.00%> (+0.16%)	⬆️
...fr/acinq/eclair/payment/relay/ChannelRelayer.scala	100.00% <100.00%> (ø)
... and 9 more

... and 3 files with indirect coverage changes