Inform users of potential manual cleanup of user-data.isos in longstanding Rancher envs.

[jakefhyde]

Related Issues

SURE-6985
rancher/rancher#25073

Summary

Some point before v2.9.2 was released, rancher/rancher#25073 no longer was reproducible. Although the issue no longer occurs, vSphere environments used by Rancher prior to v2.9.2 may still see an abundance of user-data.iso files related to infrastructure that no longer exists, which requires manual cleanup.

NOTE: While it was suggested to use a script to perform the cleanup, I personally don't think this will be doable, as a single vSphere instance can be used across multiple Rancher instances as well as standalone, so there is not a good mechanism for determining which folders/files are not in use.

[jakefhyde]

This is the messaging I am planning on adding to the docs:

vSphere node driver or custom clusters created prior to v2.9.1 may have resulted in user-data.iso files being orphaned on node deletion. This issue has since been resolved: rancher/rancher#25073, however no automatic cleanup existing for these previously orphaned files. vSphere administrators can manually remove orphaned files, however care should be taken not to remove files in use by existing machines, as this may cause outages for downstream virtual machines.