[explorer/rest]: added mosaics pagination endpoint

[AnthonyLaw]

What was the issue?

• Implement mosaics pagination endpoint.

What's the fix?

• Added mosaics pagination endpoint
• Added unit test.

[codecov]

Codecov Report

Merging #711 (c12caf1) into explorer/rest-mosaic-endpoint (5599779) will increase coverage by 0.00%.
The diff coverage is 100.00%.

Additional details and impacted files

@@                      Coverage Diff                       @@
##           explorer/rest-mosaic-endpoint     #711   +/-   ##
==============================================================
  Coverage                          98.26%   98.26%           
==============================================================
  Files                                163      163           
  Lines                               6668     6696   +28     
  Branches                             143      143           
==============================================================
+ Hits                                6552     6580   +28     
  Misses                               116      116           

Flag	Coverage Δ
explorer-nodewatch	98.40% <ø> (ø)
explorer-rest	99.64% <100.00%> (+0.03%)	⬆️
faucet-authenticator	100.00% <ø> (ø)
faucet-backend	98.91% <ø> (ø)
faucet-frontend	100.00% <ø> (ø)
lightapi-python	98.35% <ø> (ø)
tools-shoestring	96.76% <ø> (ø)
tools-vanity	99.25% <ø> (ø)

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Files	Coverage Δ
explorer/rest/rest/__init__.py	98.92% <100.00%> (+0.14%)	⬆️
explorer/rest/rest/db/NemDatabase.py	100.00% <100.00%> (ø)
explorer/rest/rest/facade/NemRestFacade.py	100.00% <100.00%> (ø)