Grab accountant promise from db while settling

[vkuznecovas]

Fixes #2295

[codecov-commenter]

Codecov Report

Merging #2299 into master will decrease coverage by 0.09%.
The diff coverage is 47.05%.

@@            Coverage Diff             @@
##           master    #2299      +/-   ##
==========================================
- Coverage   48.15%   48.06%   -0.10%     
==========================================
  Files         276      276              
  Lines       12860    12874      +14     
==========================================
- Hits         6193     6188       -5     
- Misses       6073     6090      +17     
- Partials      594      596       +2     

Impacted Files	Coverage Δ
session/pingpong/accountant_promise_settler.go	45.87% <47.05%> (-0.54%)	⬇️
p2p/channel.go	74.32% <0.00%> (-2.30%)	⬇️
nat/traversal/pinger.go	72.33% <0.00%> (-1.95%)	⬇️
tequilapi/endpoints/sse_handler.go	72.17% <0.00%> (-1.74%)	⬇️
core/discovery/discovery.go	64.75% <0.00%> (-1.64%)	⬇️
core/policy/oracle.go	91.89% <0.00%> (+5.40%)	⬆️

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