Additional support in ledger_entry

[tequdev]

close #5198

High Level Overview of Change

Context of Change

Type of Change

• [x ] New feature (non-breaking change which adds functionality)

API Impact

• [x ] Public API: New feature (new methods and/or new fields)

[codecov]

Codecov Report

Attention: Patch coverage is 82.22222% with 8 lines in your changes missing coverage. Please review.

Project coverage is 77.9%. Comparing base (0324764) to head (56d631b).

Files with missing lines	Patch %	Lines
src/xrpld/rpc/handlers/LedgerEntry.cpp	82.2%	8 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##           develop   #5236   +/-   ##
=======================================
  Coverage     77.9%   77.9%           
=======================================
  Files          783     783           
  Lines        66707   66752   +45     
  Branches      8118    8119    +1     
=======================================
+ Hits         51953   51998   +45     
  Misses       14754   14754           

Files with missing lines	Coverage Δ
src/xrpld/rpc/handlers/LedgerEntry.cpp	77.0% <82.2%> (+0.9%)	⬆️

... and 2 files with indirect coverage changes

[mvadari]

I think the API for the singletons like amendments deserves a bit more discussion. I'm not entirely convinced that a boolean is the right way to go about it (but I'm also not sure what the right way should be).