DOC-12489 magma default storage engine

[ggray-cb]

This PR covers the impact of MB-62777 making Magma with 128 vBuckets the default storage backend.

It also tackles some of the work for DOC-12778 Data Settings guidance for reader/writer threads change to 'disk i/o optimized' needs to be revised because it was in the the same area of the doc being updated anyhow. The other areas of that ticket are being handled in the DOC-12485 prevent bucket from running out of space PR.

The following pages were updated for this PR (links lead to preview site. Here's the username/password for the preview)

• What's New entry
• vBuckets edited for doc standards. Clarfiied the number of vBuckets used by storage backends/platforms. Also expanded on a few thigns, such as active vBuckets, that were glossed over in past versions.
• Storage Engines Moved Magma up to top of the topic as it's now the default. Added descriptions for the 128 vBucket version and the new default behavior. Updated the Magma Writer Thread Settings description for DOC-12778.
• Create a Bucket updated the screenshot and procedure for creating a bukcet using the GUI. Added explicite statements about teh default storage backend to the two other examples.
• Migrate a Bucket’s Storage Backend Added note that you cannot migrate a bucket from 128 vBuckets to 1024 vBuckets using the technique fo changing the storage backend setting. Added section on using XDCR to migrate between buckets with differnt numbers of vBuckets. Added example Python script to duplicate scopes/collection definitions to another bucket.
• Cross Data Center Replication(XDCR) added note about not being able to rep;icate 128 vBucket Magma to older clusters.
• Prepare for XDCR added same note as above.
• Creating and Editing Buckets added the numVBuckets parameter and updated descriptions of the default storage backend.
• Getting Bucket Information updated the example output.
• Upgrade added section on upgrade implications of new default storage backend.