Cherry-pick 0.13 migration docs to 0.13 release branch

[evankanderson]

Fixes #2275

Proposed Changes

• Cherry pick Source migrations #2275 and 💄 adding the SinkBinding bits to the index file as well... #2297

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[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: evankanderson

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[evankanderson]

/assign @n3wscott @matzew

[evankanderson]

@googlebot I consent.

[matzew]

/lgtm

[matzew]

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