[amithins]

• All tests have passed. If this feature is not already covered by the tests, new tests have been added.
• The pull request is targeting the master branch.
• The code has been validated to compile successfully by running go vet ./....
• The code has been formatted properly using go fmt ./....

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What

• jf rt transfer-plugin-install is now hidden and only logs a deprecation warning; it no longer installs anything. Its flags are accepted but ignored.
• Transfer test setup no longer installs or reloads the data-transfer plugin; the transfer workflow and docs no longer mention it.
• test.installDataTransferPlugin stays defined as a deprecated no-op so existing pipelines don't fail on an unknown flag. It can be removed in a follow-up once no workflow passes it.

Dependency

transfer-files stops requiring the plugin only with a jfrog-cli-core version that includes the GET/PUT transfer cutover. This PR must not merge before go.mod is bumped to such a version. Until then the transfer integration tests will still fail at the plugin check.