Clarify 14.1 on the upgrade path

What does this MR do?

Add emphasis to:

1. Customers on 14.0.0-14.0.4 cannot upgrade to 14.2.0 or higher without first stopping at a patched release.

   This will affect early adopters, and customers who tend to select .0 releases for their upgrade paths.

   To catch these folks, 14.1 is (back) on the upgrade path, but this documents who can actually skip it.

2. Batched migrations need to finish, or errors.

3. Apply the latest patch releases. This is implied by the migration path, but it's not clearly stated in the maintenance policy. We see folks appling the dot-zero unpatched releases on a fairly regular basis.

Follow up to a thread in another MR - !69876 (comment 690970786)

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