Betterize dataset update blurb

[blag]

This is a follow-up PR to #26815. I will rebase this on main after that PR is merged.

In that PR, in the DAGs view, we display "X of Y Datasets" for all DAGs that are scheduled on one or more datasets.

This is functionally useful except for datasets that are only ever triggered on one dataset. In that case, as long as the consuming DAG isn't paused and isn't currently running (maybe), the Next Run column will always display "0 of 1 Datasets".

Instead of doing that, for DAGs that consume only one dataset, we now simply show that URI:

The merge commit for this should also be cherry-picked after that merge commit.

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[bbovenzi]

• I added URI truncation if over 40 characters.
• Fixed a few issues with the Next run text on dag.html
• Decided to skip the tooltip text change and opening a modal when there is only one dataset. Instead, we can link directly to the dataset details