squid: doc/cephfs: Squid and later - subvolume quiesce

[zdover23]

Add a note to the "Subvolume quiesce" section that says that the information in the section applies only to the Squid and later releases of Ceph. This is included here so that I don't overwrite the Reef and Quincy documentation with irrelevant information, and so that I don't overwrite the Squid information with blank space where the "Subvolume quiesce" section should be.

Signed-off-by: Zac Dover zac.dover@proton.me
(cherry picked from commit be63ca6)

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