[rubrik] Add managed volumes datastream

[devamanv]

Proposed commit message

The PR adds a new data stream to collect the metrics for Managed Volumes. Managed Volumes provide hosts with a backup target location on a Rubrik cluster. Following are the metrics collected:

Metric	Description
Free Size	Free capacity for the volume across all the channels, in bytes.
Num Channels	Number of channels to divide the volume into. Each channel provides a unique share to write to.
Pending Snapshot Count	Pending snapshots.
Snapshot Count	Number of snapshots.
State	State of managed volume.
Storage Utilization	Used capacity for the volume across all the channels, in bytes.
Used Size	Used capacity for the volume across all the channels, in bytes.
Volume Size	Maximum capacity for the volume across all the channels, in bytes.

Checklist

• I have reviewed tips for building integrations and this pull request is aligned with them.
• I have verified that all data streams collect metrics or logs.
• I have added an entry to my package's changelog.yml file.
• I have verified that Kibana version constraints are current according to guidelines.
• I have verified that any added dashboard complies with Kibana's Dashboard good practices

Author's Checklist

• [ ]

How to test this PR locally

Related issues

• Closes https://github.com/elastic/obs-integration-team/issues/123

Screenshots

[tommyers-elastic]

i saw a previous comment about starting at 0.0.1, but incremening the minor version number for new datasets makes total sense, so i think keeping 0.1.0 -> 0.2.0 etc is good.

[tommyers-elastic]

filesets -> managed volumes

[tommyers-elastic]

12111 -> 12173

[tommyers-elastic]

sorry, i started reviewing this, but i saw it's got a load of unmodified code copied from the filesets PR. ping me when this is ready for review. thanks!