[manila-csi-plugin] Update manila dev doc regarding implemented features

[gouthampacha]

What this PR does / why we need it: Snapshotting and cloning CephFS shares is supported (#2299) so is Topology via Manila AZs (#939, #2255)

NONE

[jichenjc]

/approve

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: jichenjc

The full list of commands accepted by this bot can be found here.

The pull request process is described here

Needs approval from an approver in each of these files:

• ~~OWNERS~~ [jichenjc]

Approvers can indicate their approval by writing /approve in a comment Approvers can cancel approval by writing /approve cancel in a comment

[dulek]

/lgtm