Add equality operator for entity

[ghost]

• Validate entity for edit operations (crud & netconf service)
• Make Entity::get_children() a const method

[codecov-io]

Codecov Report

Merging #432 into master will decrease coverage by 1.69%.
The diff coverage is 92.3%.

@@            Coverage Diff            @@
##           master     #432     +/-   ##
=========================================
- Coverage   85.03%   83.33%   -1.7%     
=========================================
  Files          99      101      +2     
  Lines       11588    13371   +1783     
  Branches     1674     2010    +336     
=========================================
+ Hits         9854    11143   +1289     
- Misses       1277     1650    +373     
- Partials      457      578    +121

Impacted Files	Coverage Δ
ydkgen/printer/cpp/class_constructor_printer.py	97.4% <ø> (-0.04%)	⬇️
ydkgen/printer/cpp/class_get_children_printer.py	100% <100%> (ø)	⬆️
ydkgen/printer/cpp/class_members_printer.py	96.12% <100%> (ø)	⬆️
ydkgen/printer/cpp/class_get_child_printer.py	100% <100%> (ø)	⬆️
...dkgen/printer/cpp/class_get_entity_path_printer.py	96.35% <100%> (ø)	⬆️
ydkgen/printer/cpp/class_source_printer.py	97.97% <50%> (-0.99%)	⬇️
ydkgen/builder/test_case/test_cases_builder.py	77.69% <0%> (-3.24%)	⬇️
ydkgen/builder/test_case/test_value_builder.py	90.37% <0%> (-1.68%)	⬇️
...dk/python/core/ydk/services/_meta/_ietf_netconf.py	100% <0%> (ø)	⬆️
ydkgen/printer/cpp/class_has_data_printer.py	100% <0%> (ø)	⬆️
... and 21 more

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