Use test double for azure keyvault in system tests

[stefpiatek]

Description

For our system tests, we currently connect to an azure keyvault, we want to replace it with a docker container running something that mimics the keyvault. This will help developer setup not requiring an azure keyvault, and should decrease costs of running tests.

lowkey-vault looks like a good option, has a prebuilt docker image and test containers

Haven't deeply investigated but it looks like the auth flow should work and we can configure it with secret name & secret values for keyvault names.

The .env.sample file in the test directory will need to be updated, adding in the URI for the key vault URI. The top level docker-compose file should have a azure_uri variable that defaults to vault.azure.net if not filled passed through to hasher-api and export-api, and that is used in _setup_client() in the core project config.

Dev setup requirements

• .secrets.env values shared
• Docker and uv installed on dev machine
• test/run-system-test.sh can be run, powershell script version created, or manually run

Other options considered

• https://github.com/rokeller/azure-keyvault-emulator looks like it might also work, but is less maintained and less popular
• If all else fails, we could make a fast api app that runs in a docker container that mocks out the required functionality

Acceptance

• system test docker-compose.yml creates a container for mocking out azure keyvault with the secrets for hashing and export added.
• system test .secrets.env file is configured to connect to the mock keyvault and committed. The .secrets.env.sample file is removed
• system tests pass with no access to a real azure keyvault
• Remove all references to .secrets.env for setup instructions and in github actions

[linear-code]

PIX-76