BDMS-118: Create analysis method table

[ksmuczynski]

Why

This PR addresses the following problem / context:

• Create an AnalysisMethod table to store all the abstract methodologies used to generate data.
• Storing this information in a dedicated table ensures that every data point can be linked to a citable, defensible, and unambiguous procedure.
• This table is distinct from the Sensor (Equipment) table, as it deals with intangible procedures, not physical objects.

How

Implementation summary - the following was changed / added / removed:

• Created a new AnalysisMethod model and populated with appropriate fields and relationships.
• Updated the Observation table to include a foreign key to the AnalysisMethod table.
• Updated the Observation table to include a relationship to the AnalysisMethod table.
• Updated the lexicon.json file to include valid values for the analysis_method_type field.

Notes

Any special considerations, workarounds, or follow-up work to note?

• Related validation schema files and test files still need to be created or updated.
• Transfer script needs to be created.

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ All tests successful. No failed tests found.

Files with missing lines	Coverage Δ
db/__init__.py	97.36% <100.00%> (ø)
db/analysis_method.py	100.00% <100.00%> (ø)
db/observation.py	100.00% <100.00%> (ø)