Log the following information in email headers:
* X-Danbooru-User: the user's name and ID.
* X-Danbooru-IP: the user's IP.
* X-Danbooru-Session: the users' session ID.
* X-Danbooru-URL: the page that triggered the email.
* X-Danbooru-Job-Id: the ID of the background job that sent the email.
* X-Danbooru-Enqueued-At: when the email was queued as a background job.
* X-Danbooru-Dmail: for Dmail notifications, the link to the Dmail.
* X-Request-Id: the request ID of the HTTP request that triggered the email.
Also make it so we log an event in the APM when we send an email.
Remove the `CurrentUser.ip_addr` global variable and replace it with
`request.remote_ip`. Before we had to track the current user's IP in a
global variable so that when we edited a post for example, we could pass
down the user's IP to the model and save it in the post_versions table.
Now that we now longer save IPs in version tables, we don't need a global
variable to get access to the current user's IP outside of controllers.
* Fix `UploadService is not a class` error.
* Update list of available job classes (remove UploadPreprocessorDelayedStartJob,
UploadServiceDelayedStartJob, add ProcessUploadJob).
Fix the /jobs listing to show retried jobs. GoodJob::ActiveJobJob has a
default scope that filters out retried jobs; remove it in the index
controller so we can see retried jobs.
Also fix mail delivery jobs not showing up in the dropdown in the /jobs
search form.
Add ability to search jobs on the /jobs page by job type or by status.
Fixes#2577 (Search filters for delayed jobs). This wasn't possible
before with DelayedJobs because it stored the job data in a YAML string,
which made it difficult to search jobs by type. GoodJobs stores job data
in a JSON object, which is easier to search in Postgres.
Switch the ActiveJob backend from DelayedJob to GoodJob. Differences:
* The job worker is run with `bin/good_job start` instead of `bin/delayed_job`.
* Jobs have an 8 hour timeout instead of a 4 hour timeout.
* Jobs don't automatically retry on failure.
* Finishing jobs are preserved and pruned after 7 days.
