CI: refactor CI workflow for cloudberry-backup

[tuhaihe]

• replace the previous single-job flow with a two-stage build/test pipeline

• build Cloudberry from source and publish the install as an artifact

• run unit/integration/end_to_end tests in parallel jobs

• add Apache header and CI documentation in the workflow

• capture logs and upload artifacts on failure with a test summary

closes: #ISSUE_Number

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[tuhaihe]

Need #65 to be fixed.