Config: Expose merged configuration for easier debugging

[gmalouf]

Summary

This PR also introduces endpoint to retrieve local config in json format, scoped to private/admin API. It additionally adds a print to the algo-out file at startup of a fully hydrated/merged version of the configuration.

Test Plan

Added test for the new GetConfig endpoint.

[codecov]

Codecov Report

Attention: Patch coverage is 0% with 7 lines in your changes missing coverage. Please review.

Project coverage is 56.15%. Comparing base (3bcfedb) to head (61982e4).
Report is 1 commits behind head on master.

Files	Patch %	Lines
cmd/algod/main.go	0.00%	5 Missing ⚠️
daemon/algod/api/server/v2/handlers.go	0.00%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #6049      +/-   ##
==========================================
+ Coverage   56.13%   56.15%   +0.02%     
==========================================
  Files         488      488              
  Lines       69425    69432       +7     
==========================================
+ Hits        38973    38991      +18     
+ Misses      27796    27787       -9     
+ Partials     2656     2654       -2     

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[algorandskiy]

GetConfig REST LGTM