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Updated Flexvolume setup mechanisms for COS instance image.
- If REMOUNT_VOLUME_PLUGIN_DIR is set to true, VOLUME_PLUGIN_DIR is remounted with `exec` option during cluster startup. This allows any writable location to be used as the plugin directory.
- New HostPath added to controller-manager deployment to enable access to volume plugin directory.
- Improved how the default directory is passed to master and node setup.
**What this PR does / why we need it**: Part of the fix for #57353
/release-note-none
/sig storage
/assign @saad-ali @roberthbailey
/cc @chakri-nelluri @wongma7