Improve DAG loading in Graph view when using Dynamic Tasks

[Josersanvil]

closes: #27483

This PR just makes a small change to the function inwww that loads the DAG view for the Web UI.

Right now, the view loops and retrieves the mapped instances of all the expansions of a single task, that means that if a DAG created 100 expansions of a task instance, it loops through all the 100 expansions in order to retrieve the status of the 100! This makes the loading of that view very slow, and it is also not needed, applying the same logic, we only need to retrieve the mapped instances of one of the expansions to get the status of the rest (Since they all share the same Task Id).

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[boring-cyborg]

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[pierrejeambrun]

Indeed get_instance_with_map returns a summary for all mapped task and doesn't need to be run for each index.

Tested locally and looking good :)

[pierrejeambrun]

We might still have an issue with the try_number, but this was already the case before. (try_number is shared for a specific task_id, we will pick the value of the first mapped task returned by dag.get_task_instances, which seems weird).

edit: I just looked at the equivalent in the grid view, and we do not return a 'try_number' for mapped task summaries. (which makes sense I believe)

[hussein-awala]

Nice catch! LGTM

[boring-cyborg]

Awesome work, congrats on your first merged pull request!

[potiuk]

Sounds like a good candidate for the next PR of the month ;)

[jedcunningham]

(#protm so @potiuk's nomination gets found by the automation!)

Congrats on your first commit @Josersanvil 🎉