🚧Fix app service path resolution

[CalvinWilkinson]

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Description

Improve the directory path resolution in the AppService class.

This will involve changing the logic of the AppDirectory property to use the AppContext.BaseDirectory API instead of using the Assembly.GetExecutingAssembly() API.

The reason for this is that when using the Assembly.GetExecutingAssembly().Location API, the value is empty when publishing as a single file. This is due to where the contained binaries and dotnet files are managed and extracted to on the first execution of a single file published application.

With this change, this means content directory path resolution will work correctly when publishing as a single file.

Acceptance Criteria

The items to complete to satisfy the Definition of Done.

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1. All the unit tests have been executed and passed locally after the PR work is complete. (Why? Refer to 'Additional Information' below.)
2. The AppService has been updated
3. When performing a single file publish, the application works correctly.
4. When performing a self-contained publish, the application works correctly.

ToDo Items

The items to complete to satisfy the Definition of Done.

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1. Add a change type label to the issue. Refer to the Change Type Labels section below.
2. Add a priority label to the issue. Refer to the Priority Type Labels section below.
3. Link the issue to the correct milestone (if applicable).

Issue Dependencies

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Related Work

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Additional Information:

Unit Tests

Reasons for local unit test execution:

• Unit tests might pass locally but not in the CI environment during the status check process or vice-versa.
• Tests might pass on the developer's machine but not necessarily on the code reviewer's machine.
• If you notice that the test status check has passed but the test failed locally, please notify a project maintainer!

💡Warning💡
If the unit tests pass remotely and are not executed locally, this means we could be letting a bug slip into production.
Though bugs will always exist in some capacity, we should all do our part to help prevent them from happening.

Change Type Labels

Change Type	Label
Bug Fixes	🐛bug
Breaking Changes	🧨breaking-changes
New Feature	✨new-feature
CICD Changes	♻️cicd
Config Changes	⚙️config
Performance Improvements	🏎️performance
Code Doc Changes	🗒️documentation/code
Product Doc Changes	📝documentation/product

Priority Type Labels

Priority Type	Label
Low Priority	low priority
Medium Priority	medium priority
High Priority	high priority

Code of Conduct

• I agree to follow this project's Code of Conduct.