Update shards protobuf to represent multiple writable shards

[jotare]

Description

Describe the proposed changes made in this PR.

How was this PR tested?

Describe how you tested this PR.

[shortcut-integration]

This pull request has been linked to Shortcut Story #9268: Update Shards protobuf to represent multiple active shards.

[codecov]

Codecov Report

Attention: Patch coverage is 83.33333% with 1 lines in your changes are missing coverage. Please review.

Project coverage is 83.97%. Comparing base (31740e4) to head (6efc8a4).

Files	Patch %	Lines
nucliadb/nucliadb/ingest/consumer/shard_creator.py	83.33%	1 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #1927   +/-   ##
=======================================
  Coverage   83.97%   83.97%           
=======================================
  Files         329      329           
  Lines       18713    18681   -32     
=======================================
- Hits        15714    15688   -26     
+ Misses       2999     2993    -6     

Flag	Coverage Δ
ingest	68.73% <83.33%> (+<0.01%)	⬆️
sdk	87.85% <ø> (ø)
utils	82.63% <ø> (ø)

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

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.