fix: use TEXEAR_HOME or the current directory as the default working directory

[Yicong-Huang]

In our current implementation, we used the core folder as the root of all services. When looking for the configuration of a service, we search from the core folder. This logic relies heavily on the core folder. This PR changes the behavior:

1. We use TEXERA_HOME env variable to find the root of the Texera repo. All services/configures/files should be searched starting from this dir.
2. When omitted, we use the current directory as the default working directory.

fixes #3871

[Copilot]

Pull Request Overview

This PR refactors configuration path resolution to use the TEXERA_HOME environment variable instead of hardcoded relative paths. The change allows for more flexible deployment and configuration management by defaulting to the current working directory when TEXERA_HOME is not set.

• Removes hardcoded workflowComputingUnitManagingServicePath utility from PathUtils
• Updates computing unit managing service to dynamically resolve configuration paths using TEXERA_HOME

Reviewed Changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
core/config/src/main/scala/org/apache/amber/util/PathUtils.scala	Removes unused workflowComputingUnitManagingServicePath constant
computing-unit-managing-service/src/main/scala/org/apache/texera/service/ComputingUnitManagingService.scala	Replaces hardcoded path with dynamic resolution using TEXERA_HOME environment variable

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