Fix more SQLAlchemy 2.0 deprecation warnings.

[SpacemanPaul]

Still many SQLAlchemy 2.0 deprecation warnings coming out of test runs.

Reason for this pull request

Complete work begun in #1403.

Proposed changes

• Address outstanding SQLAlchemy 2.0 deprecation warnings in tests.

• Remove long deprecated datacube.storage.masking API (moved to `datacube.utils.masking around v1.8)

• Tests added / passed

• Fully documented, including docs/about/whats_new.rst for all changes

---

📚 Documentation preview 📚: https://datacube-core--1407.org.readthedocs.build/en/1407/

[codecov]

Codecov Report

Base: 91.96% // Head: 91.96% // Decreases project coverage by -0.01% ⚠️

Coverage data is based on head (de95bbb) compared to base (46ce315).
Patch coverage: 95.29% of modified lines in pull request are covered.

Additional details and impacted files

@@             Coverage Diff             @@
##           develop    #1407      +/-   ##
===========================================
- Coverage    91.96%   91.96%   -0.01%     
===========================================
  Files          133      132       -1     
  Lines        14452    14450       -2     
===========================================
- Hits         13291    13289       -2     
  Misses        1161     1161              

Impacted Files	Coverage Δ
datacube/drivers/postgis/_connections.py	83.45% <ø> (ø)
datacube/index/postgis/_datasets.py	74.81% <0.00%> (ø)
datacube/index/postgis/_products.py	93.43% <ø> (ø)
datacube/index/postgres/_products.py	94.57% <ø> (ø)
datacube/drivers/postgres/_dynamic.py	90.76% <75.00%> (+0.14%)	⬆️
datacube/drivers/postgis/_core.py	94.94% <96.00%> (-0.06%)	⬇️
datacube/drivers/postgres/_core.py	96.26% <96.87%> (-0.04%)	⬇️
datacube/drivers/postgis/_api.py	87.28% <100.00%> (ø)
datacube/drivers/postgis/sql.py	83.63% <100.00%> (ø)
datacube/drivers/postgres/_api.py	96.40% <100.00%> (+0.02%)	⬆️
... and 4 more

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[omad]

TY