network: allow to handle GetMPTData with KeepOnlyLatestState on

[AnnaShaleva]

And adjust documentation along the way.

Close #2152.

[AnnaShaleva]

@roman-khimov, finally, I found out what was wrong with the updated test. State exchange is impossible if the source node is light-weighted and has GC off, so I've used invalid configuration. I've added a note about it to our docs.

[codecov]

Codecov Report

Merging #2600 (e46ec97) into master (125c280) will increase coverage by 0.02%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master    #2600      +/-   ##
==========================================
+ Coverage   84.58%   84.60%   +0.02%     
==========================================
  Files         298      298              
  Lines       37836    37858      +22     
==========================================
+ Hits        32003    32030      +27     
+ Misses       4424     4419       -5     
  Partials     1409     1409              

Impacted Files	Coverage Δ
pkg/network/server.go	73.99% <ø> (-0.01%)	⬇️
pkg/config/protocol_config.go	85.54% <100.00%> (ø)
pkg/core/transaction/transaction.go	85.18% <0.00%> (-1.49%)	⬇️
pkg/compiler/codegen.go	92.36% <0.00%> (-0.11%)	⬇️
pkg/core/native/management.go	92.30% <0.00%> (-0.10%)	⬇️
pkg/compiler/inline.go	96.75% <0.00%> (+0.07%)	⬆️
pkg/core/dao/dao.go	80.26% <0.00%> (+0.16%)	⬆️
pkg/core/blockchain.go	82.33% <0.00%> (+0.17%)	⬆️
pkg/consensus/consensus.go	73.36% <0.00%> (+0.43%)	⬆️
... and 2 more

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