Changes

refactor(pingcap/tidb): use oci download script in post-submit jobs (#3655)

This pull request updates multiple CI pipeline scripts to streamline the
process of downloading and preparing binaries, replacing the older
artifact download script with a new OCI-based script. Additionally,
minor enhancements were made to the new script for better logging and
clarity.

### Pipeline updates to use the new OCI-based artifact download script:
* Replaced the `download_pingcap_artifact.sh` script with
`download_pingcap_oci_artifact.sh` across multiple pipeline scripts,
improving the binary download process. This includes changes to the
following files:
  - `merged_e2e_test.groovy`
  - `merged_integration_common_test.groovy`
  - `merged_integration_copr_test.groovy`
  - `merged_integration_jdbc_test.groovy`
  - `merged_integration_mysql_test.groovy`
  - `merged_integration_nodejs_test.groovy`
  - `merged_integration_python_orm_test.groovy`

* Introduced a `bin` directory context in each pipeline's `Prepare`
stage to better organize binary files during the download process.
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[[3]](diffhunk://#diff-968b4ab90556db2a81de172cb4dc966a63137139794bdc10be81ed3238317b3eR72-R84)
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[[7]](diffhunk://#diff-06bad8ed948ff470e5b41a84f45d7da3d200cfc38d4144b51b3611404d0ca4feL65-R77)

### Enhancements to the OCI artifact download script
(`download_pingcap_oci_artifact.sh`):
* Added a log message to display the blob fetching URL for better
traceability during downloads.
* Improved the formatting of artifact information logs for clarity.
 (commit: 73231fb)