Changes

fix: update oci registry for tici and adjust component ci params in pr title (#4113)

This pull request updates the way OCI artifact tags are computed and
used in the integration test pipeline for TiDB. It introduces a new
function to generate normalized OCI tags based on pull request
information, updates the pipeline script to use these tags for component
downloads, and removes now-unnecessary tag normalization logic from the
artifact download script.

**Pipeline improvements and tag computation:**

* Added a new function `computeArtifactOciTagFromPR` in
`component.groovy` to generate normalized OCI tags for components based
on PR branch and title.
* Updated `pull_integration_tici_test/pipeline.groovy` to compute and
use per-component OCI tags (`OCI_TAG_PD`, `OCI_TAG_TIFLASH`, etc.) for
artifact downloads, ensuring more accurate and consistent binary
selection.
* Set the `OCI_ARTIFACT_HOST` environment variable in the pipeline for
consistent artifact registry usage.

**Pipeline directory and script usage updates:**

* Changed working directories in the pipeline to point directly to
`tidb/tests/integrationtest2/third_bin` and
`tidb/tests/integrationtest2`, simplifying paths and script invocations
for both preparation and test stages.
[[1]](diffhunk://#diff-3b125777f9fb0d8960fc2741f15aec47389b27dd72fc7af3ade75bb04171faa2L40-R63)
[[2]](diffhunk://#diff-3b125777f9fb0d8960fc2741f15aec47389b27dd72fc7af3ade75bb04171faa2L96-R95)

**Artifact download script simplification:**

* Removed the `normalize_oci_tag` function and all related normalization
calls from `download_pingcap_oci_artifact.sh`, as tags are now
pre-normalized in the pipeline logic.
[[1]](diffhunk://#diff-7b89de90e7a898ae02c7d1a2fb38fc2cfca7a9d02aa0c984930a8ef9d4174295L74-L80)
[[2]](diffhunk://#diff-7b89de90e7a898ae02c7d1a2fb38fc2cfca7a9d02aa0c984930a8ef9d4174295L272-L287)
 (commit: fd8964e)