Feat/version2.0 hierarchy

[lfbrehm]

This adds the missing GetHierarchy gRPC request, missing middlelayer tests and some bugfixes discovered while testing.

[codecov]

Codecov Report

Patch coverage: 50.68% and project coverage change: +7.02% 🎉

Comparison is base (68c3125) 36.63% compared to head (a875f46) 43.65%.
Report is 1 commits behind head on feat/version2.0rework.

❗ Current head a875f46 differs from pull request most recent head 745d6c7. Consider uploading reports for the commit 745d6c7 to get more accurate results

Additional details and impacted files

@@                    Coverage Diff                    @@
##           feat/version2.0rework     #102      +/-   ##
=========================================================
+ Coverage                  36.63%   43.65%   +7.02%     
=========================================================
  Files                         56       57       +1     
  Lines                       5713     5818     +105     
=========================================================
+ Hits                        2093     2540     +447     
+ Misses                      3620     3278     -342     

Files Changed	Coverage Δ
src/caching/cache.rs	68.20% <0.00%> (-2.24%)	⬇️
src/grpc/relations.rs	0.00% <0.00%> (ø)
src/middlelayer/clone_request_types.rs	0.00% <0.00%> (ø)
src/utils/cache_utils.rs	0.00% <0.00%> (ø)
src/utils/grpc_utils.rs	26.25% <0.00%> (ø)
src/middlelayer/update_db_handler.rs	95.55% <94.73%> (+95.55%)	⬆️
src/middlelayer/relations_db_handler.rs	87.80% <100.00%> (ø)
src/middlelayer/snapshot_db_handler.rs	100.00% <100.00%> (+16.66%)	⬆️
src/middlelayer/snapshot_request_types.rs	88.20% <100.00%> (+32.48%)	⬆️
src/middlelayer/update_request_types.rs	93.57% <100.00%> (+93.57%)	⬆️
... and 1 more

... and 5 files with indirect coverage changes

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[das-Abroxas]

Just a small note on style. Apart from that, I didn't notice anything obvious. Approved ✌️

[das-Abroxas]

Can we please not name variables with a single character? It won't break anyone's neck, but it will make it unnecessarily more difficult for later when you have to touch the code again for some reason. I have already seen this in the PR in several places.