[docs]: growpart should note that it does not work with LVM.

# Documentation request

After many hours of trying to understand why my VMs had too small partitions, I have come to the conclusion that the growpart module does not work with LVM. I expected it to, because the docs mentions LVM in a positive air with no warning:

> Note that this only works if the partition to be resized is the last one on a disk with classic partitioning scheme (MBR, BSD, GPT). LVM, Btrfs and ZFS have no such restrictions.

https://github.com/canonical/cloud-init/blob/4f60ff099eb0a6f57595706f4d34cf713d3c02b1/cloudinit/config/cc_growpart.py#L35-L37

We should change the docs to make this clearer!

## Other references

The Red Hat docs notes this:

https://access.redhat.com/documentation/en-us/red_hat_enterprise_linux/8/html-single/configuring_and_managing_cloud-init_for_rhel_8/index#troubleshooting-cloud-init_configuring-cloud-init

I also found this answer on serverfault, indicating the same thing: https://serverfault.com/a/895879/116925

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*Reported from: https://cloudinit.readthedocs.io/en/latest/index.html*