Backport of ui: use task state to determine if task is active into release/1.3.x

[hc-github-team-nomad-core]

Backport

This PR is auto-generated from #14224 to be assessed for backporting due to the inclusion of the label backport/1.3.x.

The below text is copied from the body of the original PR.

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The current implementation uses the task's finishedAt field to determine
if a task is active of not, but this check is not accurate. A task in
the "pending" state will not have finishedAt value but it's also not
active.

This discrepancy results in some components, like the inline stats chart
of the task row component, to be displayed even whey they shouldn't.

[github-actions]

Ember Test Audit comparison

	release/1.3.x	b835eff	change
passes	1301	1301	0
failures	0	0	0
flaky	0	0	0
duration	9m 30s 114ms	9m 51s 288ms	+21s 174ms

[github-actions]

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