This commit adds the initial document for version two index templates. Since these are intended to
be used in favor of V1 index templates, this re-uses the anchors for index templates to point to the
V2 APIs, renaming the V1 template docs' anchors (this was a suggestion from the docs team).
There is more documentation that can be written, but this is a start.
Relates to #53101
debadair
Lisa Cawley
Lee Hinman
James Rodewig