Spine Items changes related to ditching Dagster

[ptsavol]

Re spine-tools/Spine-Toolbox#2523

Checklist before merging

• [x] Documentation (also in Toolbox repo) is up-to-date
• [x] Release notes in Toolbox repo have been updated
• [x] Unit tests have been added/updated accordingly
• [x] Code has been formatted by black
• [x] Unit tests pass

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 50.00000% with 3 lines in your changes are missing coverage. Please review.

Project coverage is 61.74%. Comparing base (1ea1f1f) to head (1ec6075).

Files	Patch %	Lines
spine_items/db_writer_item_base.py	50.00%	1 Missing :warning:
spine_items/exporter/exporter.py	50.00%	1 Missing :warning:
spine_items/tool/tool.py	50.00%	1 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## 0.8-dev #204 +/- ## =========================================== + Coverage 61.71% 61.74% +0.02% =========================================== Files 190 190 Lines 17685 17687 +2 Branches 2897 2897 =========================================== + Hits 10914 10920 +6 + Misses 6187 6183 -4 Partials 584 584 ```

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