Apply the changed requirement for the Admin endpoints

[linked0]

Added the new login endpoint and changed the name and return value for the existing validator and encriptionkey endpoints.

Relates #3280

[codecov[bot]]

Codecov Report

Merging #3294 (514c280) into v0.x.x (be9b8d1) will increase coverage by 1.00%. The diff coverage is 0.00%.

@@            Coverage Diff             @@
##           v0.x.x    #3294      +/-   ##
==========================================
+ Coverage   87.83%   88.84%   +1.00%     
==========================================
  Files         164      165       +1     
  Lines       16964    17081     +117     
==========================================
+ Hits        14901    15176     +275     
+ Misses       2063     1905     -158     

Flag	Coverage Δ
integration	40.31% <0.00%> (?)
unittests	87.59% <0.00%> (-0.25%)	:arrow_down:

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
source/agora/node/admin/AdminInterface.d	52.54% <0.00%> (ø)
source/agora/common/Task.d	88.88% <0.00%> (-11.12%)	:arrow_down:
source/agora/consensus/BlockStorage.d	68.90% <0.00%> (-8.49%)	:arrow_down:
source/agora/test/NetworkDiscovery.d	84.09% <0.00%> (-4.55%)	:arrow_down:
source/agora/consensus/protocol/Nominator.d	90.94% <0.00%> (-0.72%)	:arrow_down:
source/agora/consensus/state/Ledger.d	88.85% <0.00%> (-0.66%)	:arrow_down:
source/agora/node/Validator.d	91.45% <0.00%> (-0.47%)	:arrow_down:
source/agora/flash/Node.d	80.67% <0.00%> (-0.43%)	:arrow_down:
source/agora/node/TransactionRelayer.d	89.09% <0.00%> (-0.20%)	:arrow_down:
source/agora/network/Client.d	88.13% <0.00%> (-0.10%)	:arrow_down:
... and 13 more

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