[DOC]Add share groups and share group snapshots quotas

[OpenStack Infra]

https://review.openstack.org/473464
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commit 256b5c84ba6f2fa42c72d0ab50c906d8dcf2f986
Author: Valeriy Ponomaryov <email address hidden>
Date: Fri Jun 9 20:03:06 2017 +0300

    Add share groups and share group snapshots quotas

    "Quota" APIs now will return two new following keys:

    - 'share_groups'
    - 'share_group_snapshots'

    For user and project, but not share type.
    Default values can be configured using following config options:

    - 'quota_share_groups'
    - 'quota_share_group_snapshots'

    APIImpact
    DocImpact
    Implements BluePrint add-share-groups-quota
    Change-Id: I397a8e886226cb22fa50abdf2a4a938bb04c655d

[zhongjun (jun-zhongjun)]

Added share groups and share group snapshots quotas api in https://review.openstack.org/#/c/491700/

[zhongjun (jun-zhongjun)]

Added share groups and share group snapshots quotas doc in https://review.openstack.org/#/c/514080/

[Goutham Pacha Ravi (gouthamr)]

These fixes were released in Queens: https://review.opendev.org/#/c/514080/5/doc/source/admin/shared-file-systems-quotas.rst
https://docs.openstack.org/manila/queens/admin/shared-file-systems-quotas.html