Read allowlist templates from correct path

[llewelld]

✅ Checklist

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🚦 Depends on

N/A.

⤴️ Summary

The allowlist templates were being read from a path relative to the CWD. This meant that they would be correctly output, but only if the command was run from inside the root of the data-save-haven working directory. This updates the code to read the files correctly from the resource directory irrespective of the CWD.

🌂 Related issues

Closes #2533

🔬 Tests

Tested by running the following commands:

cd data-safe-haven
dsh allowlist template pypi
pushd ..
dsh allowlist template pypi
popd

Previously the second call to dsh would generate an error, but after this change it no longer does. I've also added a new unit test to perform roughly the same check (changes directory, requests template, restores directory). The test fails with previous versions of the code but passes after the changes here.

I specifically chose this issue while I'm awaiting access to the dev SRE, because it only relies on code running locally (and it was an easy fix while I get familiar with the code and processes).

[github-actions]

Coverage report

Click to see where and how coverage changed

File	Statements	Missing	Coverage	Coverage (new stmts)	Lines missing
data_safe_haven/commands
allowlist.py					133-134
data_safe_haven/utility
file_reader.py
Project Total

This report was generated by python-coverage-comment-action

[cptanalatriste]

Looks good to me!

[llewelld]

Thanks for looking at this @cptanalatriste. Is one review enough to have this merged? If so, I'm not authorised to merge myself, would you mind please merging it for me?