UI: Add rendering of poststop tasks

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This adds a new poststop lifecycle phase:

It relies on #8194.

[github-actions]

Ember Asset Size action

As of dd34ab2

Files that got Bigger 🚨:

File	raw	gzip
nomad-ui.js	+394 B	+55 B
nomad-ui.css	+320 B	+41 B

Files that stayed the same size 🤷‍:

File	raw	gzip
auto-import-fastboot.js	0 B	0 B
vendor.js	0 B	0 B
vendor.css	0 B	0 B

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Ember Test Audit comparison

	master	dd34ab2	change
passes	1425	1425	0
failures	0	0	0
flaky	0	0	0
duration	5m 29s 138ms	5m 25s 626ms	-03s 512ms

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I’ve tried this locally with a dev build of this branch and it works:

So I think it can be reviewed but we can hold off merging until that branch is ready.

[github-actions]

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