feat: make inner container name configurable via CODER_CVM_CONTAINER_NAME

[blinkagent]

Summary

The inner container name is currently hardcoded to workspace_cvm and cannot be changed. There is already an environment variable constant CODER_CVM_CONTAINER_NAME defined in the code, but it is never used to override the container name.

Current Behavior

The container name is hardcoded:

InnerContainerName = "workspace_cvm"

And used directly when creating the container:

containerID, err := dockerutil.CreateContainer(ctx, client, &dockerutil.ContainerConfig{
    // ...
    Name: InnerContainerName,
    // ...
})

Proposed Solution

Leverage the existing CODER_CVM_CONTAINER_NAME environment variable to allow users to configure the inner container name. If not set, default to the current workspace_cvm.

Use Case

Users may want to customize the container name for organizational purposes, logging clarity, or to avoid conflicts in environments where multiple envbox instances are running.

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Issue created on behalf of a customer request.