feat: make SQLAlchemy pool class configurable + add tracer to db.py and dbview.py

[thinkh]

Related issue: https://github.com/Caleydo/tdp_bi_bioinfodb/issues/1439

Developer Checklist (Definition of Done)

Issue

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• Tested in latest Chrome/Firefox

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PR

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Summary of changes

• make SQLAlchemy pool class configurable
• add tracer to db.py and dbview.py

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