Change exec URLs to use job’s namespace/region

[backspace]

This closes #9966. It was looking at the query parameters
for the namespace and region, but allocation (and task!)
routes don’t have a namespace query parameter. Since the URL
generator requires the job for all calls, it makes sense to
extract the namespace and region from the job instead.

[github-actions]

Ember Asset Size action

As of 3619d53

Files that got Bigger 🚨:

File	raw	gzip
nomad-ui.js	+67 B	+40 B

Files that stayed the same size 🤷‍:

File	raw	gzip
vendor.js	0 B	0 B
nomad-ui.css	0 B	0 B
vendor.css	0 B	0 B

[github-actions]

Ember Test Audit comparison

	master	3619d53	change
passes	1551	1551	0
failures	0	0	0
flaky	0	0	0
duration	8m 16s 817ms	7m 38s 905ms	-37s 912ms

[DingoEatingFuzz]

Wow, quick turnaround on this. Nice work.

[github-actions]

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