I could have split this into several commits:
* DRY direct linking to images.
* Check S3 config before direct linking.
* Just check if service is public instead of relying on name.
Developers may copy a staging or production database or experiment with
S3 storage. But when the S3 config is missing then calling `service`
raises an ArgumentError due to a missing name.
Now we only try to call `service` if the S3 config is present.
Defining an alternate s3 configuration set to `public: true` means we can use it selectively. It sets the objects to `acl: "public-read"` by default (read-only) and means any image tags for those assets can use direct public links in the src attribute (without hitting the ActiveStorage::Representation endpoint). The default non-public service will still be used by default for any other files on instances using s3.
We were also patching ActiveRecord::Relation for the `#find_by_param`
methods but we are not using those any more. They were deprecated a
while ago. We now use `find_by(permalink: ...)`.
