wfctl infra commands should support plugin-dir override for isolated verification

[intel352]

Problem

wfctl plugin install supports -plugin-dir, but wfctl infra apply does not. During workflow-compute verification, I could install a clean plugin set into /tmp/.../data/plugins, but could not run wfctl infra apply --dry-run against that isolated directory:

flag provided but not defined: -plugin-dir

Desired behavior

• Infra commands that load external plugins should accept the same plugin directory override as plugin install/list/update.
• The option should be consistently named -plugin-dir, with deprecated -data-dir alias only if existing command surfaces already expose it.
• This lets CI and local smoke tests run isolated plugin installs without mutating repo data/plugins.

Related

• wfctl plugin install should remove stale executables before extracting new plugin versions #637 tracks stale executable cleanup in default plugin dirs.