Document Fast Initial Split in 4.0

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Original Description

We're backporting the fast initial split project to 4.0, and we'd like to make sure the feature is advertised in the 4.0 docs as soon as it lands in a released version. Creating this ticket to track.
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Description

Scope of changes (files that need work and how much)

Add command/operation specific level change + tip

• source/reference/command/shardCollection.txt
• source/reference/method/sh.shardCollection.txt

• source/reference/command/addShardToZone.txt
• source/reference/method/sh.addShardToZone.txt
• source/reference/method/sh.addShardTag.txt

• source/reference/command/updateZoneKeyRange.txt
• source/reference/method/sh.updateZoneKeyRange.txt
• source/reference/method/sh.addTagRange.txt

Add general blurb/tip

• source/sharding.txt
• core/sharding-balancer-administration (Decided against)
• source/tutorial/manage-shard-zone.txt
• source/tutorial/sharding-high-availability-writes.txt
• source/tutorial/sharding-segmenting-data-by-location.txt
• source/tutorial/sharding-segmenting-shards.txt
• source/tutorial/split-chunks-in-sharded-cluster.txt

• h3: Add initial chunk information (missing not just for initial zone setup)

• source/core/hashed-sharding.txt
• source/core/ranged-sharding.txt
• source/core/zone-sharding.txt
• core/sharding-data-partitioning
• tutorial/create-chunks-in-sharded-cluster/ (but can reference core/sharding-data-partitioning)
• /tutorial/split-chunks-in-sharded-cluster (but can reference core/sharding-data-partitioning)

Impact to other docs outside of this product

None – we don't talk about initial chunks/distributions in Atlas/OpsMgr/CloudMgr docs

MVP (work and date?)

Resources (e.g. Scope Docs, Invision)