refactor datamanager usage to be consistent

[vangheem]

move txn management out of it for now

Description

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How was this PR tested?

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[codecov]

Codecov Report

Attention: Patch coverage is 62.50000% with 12 lines in your changes are missing coverage. Please review.

Project coverage is 83.83%. Comparing base (ad37d53) to head (d333a7e).
Report is 2 commits behind head on main.

Files	Patch %	Lines
nucliadb/nucliadb/ingest/orm/knowledgebox.py	52.38%	10 Missing ⚠️
nucliadb/nucliadb/ingest/orm/processor/__init__.py	50.00%	1 Missing ⚠️
nucliadb/nucliadb/ingest/service/writer.py	50.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1974      +/-   ##
==========================================
- Coverage   83.98%   83.83%   -0.15%     
==========================================
  Files         329      328       -1     
  Lines       18681    18166     -515     
==========================================
- Hits        15689    15230     -459     
+ Misses       2992     2936      -56     

Flag	Coverage Δ
ingest	68.71% <62.50%> (-0.09%)	⬇️
sdk	87.85% <ø> (ø)
utils	82.70% <ø> (+0.07%)	⬆️

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[sentry-io]

Suspect Issues

This pull request was deployed and Sentry observed the following issues:

• ‼️ Exception: [/usr/local/cargo/git/checkouts/client-rust-5a1ccd35a54db20f/eb1d2da/tikv-client-pd/src/timestamp... nucliadb.search.api.v1.chat.chat_knowledgebox_e... View Issue
• ‼️ Exception: gRPC error: RpcFailure: 14-UNAVAILABLE upstream connect error or disconnect/reset before headers.... nucliadb.search.api.v1.knowledgebox.knowledgebo... View Issue
• ‼️ TimeoutError: gRPC error: RpcFailure: 4-DEADLINE_EXCEEDED Deadline Exceeded nucliadb.search.api.v1.search.search_knowledgebox View Issue

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