Implement AuthorizationService

[das-Abroxas]

This implements the missing gRPC functions of the AuthorizationService.

Features:

• Permissions on resources can now get fetched, removed and updated
• After many tries Clippy convinced me to implement the Default trait for Cache

[codecov]

Codecov Report

Patch coverage: 36.55% and project coverage change: +0.15% 🎉

Comparison is base (b5f9095) 37.95% compared to head (061988b) 38.11%.
Report is 13 commits behind head on feat/version2.0rework.

Additional details and impacted files

@@                    Coverage Diff                    @@
##           feat/version2.0rework     #111      +/-   ##
=========================================================
+ Coverage                  37.95%   38.11%   +0.15%     
=========================================================
  Files                         60       60              
  Lines                       7556     7792     +236     
=========================================================
+ Hits                        2868     2970     +102     
- Misses                      4688     4822     +134     

Files Changed	Coverage Δ
src/auth/permission_handler.rs	0.00% <0.00%> (ø)
src/auth/token_handler.rs	0.00% <0.00%> (ø)
src/caching/notifications_handler.rs	0.00% <0.00%> (ø)
src/caching/structs.rs	15.38% <0.00%> (-12.21%)	⬇️
src/grpc/authorization.rs	0.00% <0.00%> (ø)
src/grpc/notification.rs	0.00% <0.00%> (ø)
src/grpc/object.rs	0.00% <0.00%> (ø)
src/main.rs	0.68% <0.00%> (-0.03%)	⬇️
src/middlelayer/create_db_handler.rs	72.00% <0.00%> (-6.27%)	⬇️
src/middlelayer/user_db_handler.rs	45.96% <0.00%> (-10.97%)	⬇️
... and 8 more

... and 2 files with indirect coverage changes

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[lfbrehm]

LGTM

[St4NNi]

I think it LGTM ...really sure !