[#7875] Fix attachment processing #7932

We're going to make a change which might mean attachments might be rebuilt within the `FoiAttachmentMaskJob` this means the signed global ID might not return the attachment in this controller. This change ensures their is a referer parameter and if the attachment can't be loaded then we redirect back to the referer. Note, we don't need to worry about people modifying the referer to get users redirected to a third party domain as this is protected against by Rails.

This check isn't doing anything. It was meant to protect when parsing incoming messages to stop hidden attachments from being made public again. We don't actually yet have this parsing in place instead we've focused on finding the original attachment [1]. For the remainder of cases we will need to parse the raw email again but we have added separate check [2] so this one here is redundant. [1] #7875 [2] #7920

Catch and rescue from `MissingAttachment` exceptions. Re-parse the incoming message to rebuild the attachments instead. Fixes: #7875

When attachment is unmasked we attempt to run the mask job inline. This commit makes a couple of changes. 1. It unlocks the job so we can run it, so we don't have to worry about if the job doesn't run 2. Now the mask job can call `IncomingMessage#parse_raw_email!(true)` we need to handle to case where the attachment disappears after being rebuilt. This results in a `ActiveRecord::RecordNotFound` when reloading the instance. 3. Add RebuiltAttachment exception which we can then catch and rescue later. See the next commit.

When calling `FoiAttachment#body` this can now raise an exception due to the current attachment instance getting replaced and no longer existing in the database. We can catch and rescue from this by reloading the new attachment and calling the same code again. This is what `FoiAttachment.protect_against_rebuilt_attachments` does and should prevent exceptions when viewing requests which haven't be masked and cached yet. These will normally be very old attachments as this also need the `hexdigest` to be mismatched.

Exception notifications don't include the name of the exception so improve the message to make it clearer what the issue is.

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[#7875] Fix attachment processing #7932

[#7875] Fix attachment processing #7932

Commits on Oct 2, 2023