Improve error reporting when loading the Docker configuration file

[0xced]

What does this PR do?

This pull request improves error handling while reading the Docker context configuration file. It throws a new DockerConfigurationException instead of silently failing.

Also, since GetCurrentEndpoint() can't return null anymore there's no need to try the default GetSocketPathFromHomeDesktopDir() and GetSocketPathFromHomeRunDir() socket paths.

Why is it important?

Silently returning null instead of throwing proper exceptions makes it harder to diagnose issues.

Related issues

• Relates feat: Get Docker endpoint from Docker context #1235

How to test this PR

The DockerConfigTests were updated and a new ThrowsWhenDockerConfigEndpointNotFound test was added.

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