Add doc for importing and unmanaging DATA volumes

[weizhouapache]

this is the document for apache/cloudstack#8808

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📚 Documentation preview 📚: https://cloudstack-documentation--390.org.readthedocs.build/en/390/

[weizhouapache]

https://cloudstack-documentation--390.org.readthedocs.build/en/390/adminguide/storage.html#importing-and-unmanaging-volumes-from-storage-pools

[kiranchavala]

@weizhouapache can we mention that only qcow2 format data volumes are supported for import and raw and other image formats are not supported.

The format of qcow2 can be checked by executing the command

qemu-img info <>

--
Also, can we mention encrypted volumes are not supported

[weizhouapache]

@weizhouapache can we mention that only qcow2 format data volumes are supported for import and raw and other image formats are not supported.

The format of qcow2 can be checked by executing the command

qemu-img info <>

-- Also, can we mention encrypted volumes are not supported

thanks @kiranchavala
I will update

[weizhouapache]

@weizhouapache can we mention that only qcow2 format data volumes are supported for import and raw and other image formats are not supported.

The format of qcow2 can be checked by executing the command

qemu-img info <>

-- Also, can we mention encrypted volumes are not supported

added to notes
thanks @kiranchavala

[kiranchavala]

LGTM, the doc for import data volumes looks good