fix: detect Docker host from context when DOCKER_HOST is not set

[Itx-Psycho0]

Solution

Added Docker context detection by running docker context inspect to get the current context's Docker endpoint when DOCKER_HOST is not set. This allows func to automatically discover the correct socket path from Docker Desktop contexts.

Changes

• Added getDockerContextHost() function in pkg/docker/docker_client.go that:
  -Runs docker context inspect command
  -Parses JSON output to extract the Docker endpoint
  -Returns the endpoint or an empty string if unavailable

• Updated NewClient() to check Docker context before falling back to default socket

• Added test case TestNewClient_DockerContext to verify the functionality

Detection Priority Order

1 DOCKER_HOST environment variable (if set)
2 Current Docker context endpoint (new)
3 Default socket path
4 Podman detection (existing fallback)

Testing

✅ All unit tests pass
✅ Linting checks pass
✅ Backward compatible with existing behavior
✅ Works with Docker Desktop on Mac and Linux

Usage

Users no longer need to manually set DOCKER_HOST when using Docker Desktop. The tool will automatically detect the correct socket from the active Docker context.

Fixes #2226

[knative-prow]

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[knative-prow]

Hi @Itx-Psycho0. Thanks for your PR.

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[Itx-Psycho0]

Hi maintainers,

I've implemented a fix for issue #2226 that adds Docker context detection when DOCKER_HOST is not set.

Summary:
Added automatic detection of Docker endpoint from the current Docker context
Fixes Docker Desktop compatibility on Mac and Linux
Maintains full backward compatibility
All tests pass

The solution runs docker context inspect to get the current context's endpoint, which allows func to work with Docker Desktop's context-specific sockets without requiring users to manually set DOCKER_HOST.

I'd appreciate your review when you have a chance.

@lkingland @dprotaso @matejvasek

Thanks!