replace SQL test fixture with imperative setup of DB records

[majewsky]

This removes the only known usage of easypg.LoadSQLFile() in the wild, thus opening up a refactoring opportunity for me.

[github-actions]

Merging this branch will not change overall coverage

Impacted Packages	Coverage Δ	🤖
github.com/sapcc/castellum/internal/api	88.85% (ø)
github.com/sapcc/castellum/internal/test	0.00% (ø)

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Coverage by file

Changed files (no unit tests)

Changed File	Coverage Δ	Total	Covered	Missed	🤖
github.com/sapcc/castellum/internal/test/setup.go	0.00% (ø)	0	0	0

Please note that the "Total", "Covered", and "Missed" counts above refer to code statements instead of lines of code. The value in brackets refers to the test coverage of that file in the old version of the code.

Changed unit test files

• github.com/sapcc/castellum/internal/api/assets_test.go
• github.com/sapcc/castellum/internal/api/errors_test.go
• github.com/sapcc/castellum/internal/api/operations_test.go
• github.com/sapcc/castellum/internal/api/resources_test.go
• github.com/sapcc/castellum/internal/api/shared_test.go