Display count of task runs by state on flow run page

[EmilRex]

First check

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Prefect Version

2.x

Describe the current behavior

Users can see a list of task runs on a flow run's page (in the Task Runs tab). It is not possible to see how many tasks are in each possible state. This becomes problematic when there are 100s or 1000s of tasks. In order to determine how many tasks are in each state, the user must apply each state filter and keep track of the counts.

Describe the proposed behavior

It would be super helpful if we could display a count of tasks in each state somewhere at the top of the Task Runs tab on the flow run page. For example, where it says n Task runs, perhaps it could say n Task runs (all Completed) or n Task runs (x Completed, y Failed). How it's surfaced is less important than whether it's surfaced at all.

Example Use

No response

Additional context

Replaces #8028