Rename new shard-manager service to shard-distributor

[jakobht]

What changed?
Renamed the new shard-manager service to shard-distributor

Why?
We want to split the shard management system in two service, shard-distributor and a load-balancer. Also there is already a shard manager struct in the code, which would be quite confusing

How did you test it?
Unit tests

Potential risks
The change is NOT backwards compatible, the service is still prototyping so noone show rely on it. We need to change the names internally when we pull in this change.

Release notes

Documentation Changes

[codecov]

Codecov Report

Attention: Patch coverage is 66.66667% with 2 lines in your changes missing coverage. Please review.

Project coverage is 81.29%. Comparing base (a6c36bf) to head (e385981).
Report is 9 commits behind head on master.

Files with missing lines	Patch %	Lines
common/service/metrics.go	0.00%	2 Missing ⚠️

Additional details and impacted files

Files with missing lines	Coverage Δ
common/service/name.go	100.00% <ø> (ø)
service/sharddistributor/service.go	94.23% <100.00%> (ø)
common/service/metrics.go	0.00% <0.00%> (ø)

... and 21 files with indirect coverage changes

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