cli: allow to provide single node config file

[AnnaShaleva]

Close #2978.

[codecov]

Codecov Report

Merging #3014 (aa76ac3) into master (abf3ef5) will decrease coverage by 0.09%.
The diff coverage is 100.00%.

❗ Current head aa76ac3 differs from pull request most recent head 4be9e43. Consider uploading reports for the commit 4be9e43 to get more accurate results

@@            Coverage Diff             @@
##           master    #3014      +/-   ##
==========================================
- Coverage   84.70%   84.62%   -0.09%     
==========================================
  Files         328      328              
  Lines       43172    43176       +4     
==========================================
- Hits        36570    36538      -32     
- Misses       5110     5148      +38     
+ Partials     1492     1490       -2     

Impacted Files	Coverage Δ
cli/options/options.go	70.45% <100.00%> (+0.92%)	⬆️
cli/server/server.go	68.75% <100.00%> (ø)
cli/vm/vm.go	31.03% <100.00%> (ø)

... and 4 files with indirect coverage changes

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