Migration to sqlalchemy version 2

[stephen-riggs]

This implements the minimum changes to update sqlalchemy to version 2.
I've currently set the requirement as sqlalchemy>=2, but it's possible this would still work in version 1.4

The breaking changes from earlier versions are:

• declarative_base has moved
• Table loads need to be attributes not strings

A more complete migration of the API query functions should be done in future, but the legacy methods still currently work.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 91.99%. Comparing base (6e83211) to head (9e1a582).
Report is 1 commits behind head on main.

Additional details and impacted files

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- Coverage   91.99%   91.99%   -0.01%     
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  Files          26       26              
  Lines        3736     3735       -1     
  Branches      252      252              
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- Hits         3437     3436       -1     
  Misses        206      206              
  Partials       93       93              

[KarlLevik]

LGTM