Feature Request: Support #pickhardtpayments

[C-Otto]

Support #pickhardtpayments as described in https://github.com/renepickhardt/mpp-splitter/blob/master/Minimal%20Linearized%20min%20cost%20flow%20example%20for%20MPP.ipynb.

• compute MPP based on flow information
• combine probability and fees in cost function
• optimize N (number of piecewise linear approximations)
• what if capacity % N != 0?
• use different values for N depending on channel size?
• what if amount % quantization != 0?
• what if amount < quantization?
• limit graph to zero base fee channels
• add support for non-zero base fee channels (moved to #PickhardtPayments: add support for non-zero base fee channels #31)
• consider max_htlc for channels
• make use of mission control information (see Feature Request: Provide MissionControl data #7)
• send out MPP
• add payment loop (deal with failed parts of MPP, try those again) (blocked by Feature Request: Add practical MPP support to SendToRouteV2 lightningnetwork/lnd#5746)
• make N, quantization, ... configurable (see Document configuration file (hardcoded resolutions) #5)
• add switch to ignore fees of local channels (for outgoing payments) (moved to #PickhardtPayments: add rebalance mode #33)
• solve startup issues wrt. OR tools native library loader
• solve pitest issues wrt. OR tools native library loader
• what if there are several parallel channels and the flow picks an amount that is more than each individual channel's capacity?
• combine parallel channels?
• add known liquidity for local channels
• do not forget about disabled/broken channels straight away (set upper bound to 1 instead of 0?)
• fail everything on first INCORRECT_OR_UNKNOWN_PAYMENT_DETAILS failure
• document middleware requirement
• fix "upper bound" vs. "in flight"
• handle failures:
  • INCORRECT_OR_UNKNOWN_PAYMENT_DETAILS = 1;
  • INCORRECT_PAYMENT_AMOUNT = 2;
  • FINAL_INCORRECT_CLTV_EXPIRY = 3;
  • FINAL_INCORRECT_HTLC_AMOUNT = 4;
  • FINAL_EXPIRY_TOO_SOON = 5;
  • INVALID_REALM = 6;
  • EXPIRY_TOO_SOON = 7;
  • INVALID_ONION_VERSION = 8;
  • INVALID_ONION_HMAC = 9;
  • INVALID_ONION_KEY = 10;
  • AMOUNT_BELOW_MINIMUM = 11;
  • FEE_INSUFFICIENT = 12;
  • INCORRECT_CLTV_EXPIRY = 13;
  • CHANNEL_DISABLED = 14;
  • TEMPORARY_CHANNEL_FAILURE = 15;
  • REQUIRED_NODE_FEATURE_MISSING = 16;
  • REQUIRED_CHANNEL_FEATURE_MISSING = 17;
  • UNKNOWN_NEXT_PEER = 18;
  • TEMPORARY_NODE_FAILURE = 19;
  • PERMANENT_NODE_FAILURE = 20;
  • PERMANENT_CHANNEL_FAILURE = 21;
  • EXPIRY_TOO_FAR = 22;
  • MPP_TIMEOUT = 23;
  • INVALID_ONION_PAYLOAD = 24;
  • other/unknown