Add CephFS Manage/unmanage documentation

- Updates the drivers support matrix
- Updates the CephFS drivers documentation and highlight how the
process works and what are the known limitations.

Change-Id: I2f937358e93271fc5ad63e76cc4a9c5aa0ba3017
(cherry picked from commit 4fe2b014e52d095d333e4cdb7ffb3269974bde43)

doc/source/admin/share_back_ends_feature_support_mapping.rst

@@ -89,7 +89,7 @@ Mapping of share drivers and share features support
 +----------------------------------------+-----------------------+-----------------------+--------------------------+--------------------------+------------------------+-----------------------------------+--------------------------+--------------------+--------------------+
 |             Oracle ZFSSA               |           K           |           N           |             M            |             M            |            K           |                 K                 |            \-            |          \-        |          \-        |
 +----------------------------------------+-----------------------+-----------------------+--------------------------+--------------------------+------------------------+-----------------------------------+--------------------------+--------------------+--------------------+
-|                 CephFS                 |           M           |          \-           |             M            |             M            |            M           |                 W                 |            \-            |          \-        |          \-        |
+|                 CephFS                 |           M           |        D (2024.2)     |             M            |             M            |            M           |                 W                 |        D (2024.2)        |          \-        |          \-        |
 +----------------------------------------+-----------------------+-----------------------+--------------------------+--------------------------+------------------------+-----------------------------------+--------------------------+--------------------+--------------------+
 |                 Tegile                 |           M           |          \-           |             M            |             M            |            M           |                 M                 |            \-            |          \-        |          \-        |
 +----------------------------------------+-----------------------+-----------------------+--------------------------+--------------------------+------------------------+-----------------------------------+--------------------------+--------------------+--------------------+

doc/source/configuration/shared-file-systems/drivers/cephfs_driver.rst

@@ -49,6 +49,8 @@ The following operations are supported with CephFS backend:
   * ``read-only`` and ``read-write`` access levels are supported.
 
 - Extend/shrink share
+- Manage/unmanage shares
+- Manage/unmanage share snapshots
 - Create, delete, update and list snapshot
 - Create, delete, update and list share groups
 - Delete and list share group snapshots
@@ -511,6 +513,28 @@ server and the path to be mounted. It is of the form,
 ``{NFS-Ganesha server address}:{path to be mounted}``
 
 
+Managing existing shares and snapshots
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+Starting from the 2024.2 (Dalmatian) release, it is possible to bring both
+CephFS Native and NFS shares (subvolumes) that already exist in the Ceph
+Storage under Manila's management. The workflow will be slightly different when
+compared to the original approach:
+
+- The :ref:`share adoption process<manage_share>` should be used, but the name
+  of the subvolume must be supplied as the ``export path`` parameter, so that
+  the driver can appropriately locate the subvolume and manage it.
+- The subvolume's ``subvolume_mode`` will not be overwritten by manila.
+- The subvolumes will not be renamed in the Ceph Storage, and at the end of the
+  manage operation, their names will be preserved.
+- In case the subvolume has its current allocated size (``bytes_quota``) set
+  as infinite, please make sure specify a new ``size`` within the
+  ``driver_options`` parameter. The driver will attempt to resize the share
+  using the provided size and will fail if it is not enough.
+- While managing CephFS Snapshots, the CephFS driver will consider the size of
+  the parent share and account it as the snapshot's quota.
+
+
 Allowing access to shares
 ~~~~~~~~~~~~~~~~~~~~~~~~~