examples: port changes from C# NNS contract

[AnnaShaleva]

This PR includes changes implemented into C# NNS version (https://github.com/neo-project/non-native-contracts/blob/master/src/NameService/NameService.cs):

1. Domain registration price is dependant on domain name length. By default, short (<5 chars) domain names are available for registration only for committee.
2. Renew overload is added that accepts expiration period as an argument. This change is backwords-compatible.
3. SetAdmin and Renew events are added.

[codecov]

Codecov Report

Merging #2694 (abd332f) into master (20224cb) will increase coverage by 0.27%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #2694      +/-   ##
==========================================
+ Coverage   85.23%   85.50%   +0.27%     
==========================================
  Files         322      322              
  Lines       39398    39680     +282     
==========================================
+ Hits        33580    33928     +348     
+ Misses       4479     4423      -56     
+ Partials     1339     1329      -10     

Impacted Files	Coverage Δ
pkg/network/message.go	94.02% <0.00%> (-1.50%)	⬇️
pkg/services/notary/notary.go	82.08% <0.00%> (-0.55%)	⬇️
pkg/services/stateroot/network.go	76.71% <0.00%> (-0.32%)	⬇️
pkg/services/oracle/response.go	84.80% <0.00%> (-0.24%)	⬇️
pkg/network/server.go	73.08% <0.00%> (-0.17%)	⬇️
pkg/neorpc/errors.go	69.69% <0.00%> (ø)
pkg/rpcclient/nep11.go	0.00% <0.00%> (ø)
pkg/consensus/crypto.go	100.00% <0.00%> (ø)
pkg/rpcclient/policy.go	65.38% <0.00%> (ø)
pkg/util/slice/array.go	100.00% <0.00%> (ø)
... and 45 more

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