Speed up task failures tile

[jlowin]

This PR adjusts the task failures tile to be more performant.

Previously, the tile did the following:

• load all tasks that have failed task runs
• for each task, query for its flow
• for each task, query for all task runs and count the task runs (in the client)

Following the pattern in the failed flows tile, this PR removes the count, which dramatically simplifies the pattern and lets us avoid two complex db calls entirely.

[znicholasbrown]

I'm not able to load this tile with the 7 day filter selected, the DB still seems to be timing out. 1 option is to remove that filter option entirely, but that's not really ideal

[jlowin]

I'll look into that

[jlowin]

Appears to be ok, it was likely some unrelated pressure

[znicholasbrown]

We looked at this last night, the timeouts seem to be unrelated but will keep an eye on it.