Clarify that ontap-san-economy only supports iscsi

[NA-Scott]

Page URL

https://docs.netapp.com/us-en/trident/trident-use/ontap-san-examples.html

Page title

ONTAP SAN configuration options and examples

Summary

In the "Backend configuration options" table, row "sanType" needs to have a comment that iscsi is the only supported option for ontap-san-economy.

This will make it match with the information already listed on page https://docs.netapp.com/us-en/trident/trident-use/ontap-san.html

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