Add documentation on Active Job.

This adds documentation for the Active Job API. It includes
documentation on how to configure the queue_adapter, and how to create
new jobs. It adds links to the various other sections of the Active Job
documentation.
Merge pull request #17068 from mokhan/update-active-job-documentation

[ci-skip] Update Active Job API documentation
Disallow appended newlines when parsing as integer

\Z allows appended newlines where \z does not.
Merge pull request #17148 from mgenereu/patch-1

Disallow appended newlines when parsing as integer
[ci skip] add `test:jobs` task to testing guide
Fix style for rescue responses doc [ci skip]

 * Change 'Any ***s that are...' to 'Any *** that is...'
 * Fix style for default rescue_responses setting

This is a follow-up commit to:

 * https://github.com/rails/rails/pull/17076
 * https://github.com/yuki24/rails/commit/89b8836f2470c689f6b7d52cab3a418bb63aef26
Merge pull request #17151 from y-yagi/patch-1

[ci skip] add `test:jobs` task to testing guide
Merge pull request #17153 from yuki24/fix-doc-format-for-rescue-responses

[Railsguides] Fix style for rescue responses doc [ci skip]
Revert "Fix style for rescue responses doc [ci skip]"

Reason: There is a wrong newline, a typo, and the change
to singular is not good.

This reverts commit d76380cf1ccec7ffeff19827ae9b6d9b71327418.
minor fixes in the configuring guide [ci skip]