Add type information for scalar values

[soininen]

Floats, booleans and strings now have explicit types in parameter_definition, parameter_value and list_value tables. This means that the values now always carry the type information with them; only when the value is None, the type is None as well.

Implements #356

Checklist before merging

• [x] Documentation (also in Toolbox repo) is up-to-date
• [x] Release notes 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 86.66667% with 10 lines in your changes missing coverage. Please review.

Project coverage is 78.24%. Comparing base (c630744) to head (5a8b129).

Files	Patch %	Lines
...versions/ca7a13da8ff6_add_type_info_for_scalars.py	84.37%	3 Missing and 2 partials :warning:
spinedb_api/parameter_value.py	87.50%	2 Missing and 3 partials :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #422 +/- ## ========================================== + Coverage 78.23% 78.24% +0.01% ========================================== Files 72 73 +1 Lines 9550 9597 +47 Branches 2039 2048 +9 ========================================== + Hits 7471 7509 +38 - Misses 1741 1746 +5 - Partials 338 342 +4 ```

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[soininen]

This should not be merged before SpineInterface has been updated accordingly.