Adding configuration to use custom delegate script with Cantaloupe

[dannylamb]

Part of Islandora/documentation#2011

Test it by setting REPOSITORY=islandora and TAG=c7f8e0e65164eeec89c5749db2e2e7aea7033eaf. Everything should continue to work as normal, and if you tail the Cantaloupe logs, you should see blurbs about it loading the delegate script. I see stuff like this:

cantaloupe_1  | 2021-12-16T14:21:34.891984512Z 14:21:34.891 [main] INFO  e.i.l.c.ApplicationContextListener - 🍈 Starting Cantaloupe 4.1.5
cantaloupe_1  | 2021-12-16T14:21:34.898643127Z 14:21:34.898 [main] INFO  e.i.l.c.s.HeapInvocationCache - Invocation cache limit: 1786880
cantaloupe_1  | 2021-12-16T14:21:35.158615467Z 14:21:35.158 [main] INFO  e.i.l.c.s.DelegateProxy - Loading script code

Followed by this during the requests, which proves the delegate is firing:

cantaloupe_1  | 2021-12-16T14:40:36.887902182Z 14:40:36.884 [http-nio-8080-exec-3] DEBUG e.i.l.c.s.DelegateProxy - invokeUncached(): httpsource_resource_info() returned {"uri"=>"https://islandora.traefik.me/sites/default/files/2021-04/armindafixcrop2.jpg", "headers"=>{"sec-fetch-mode"=>"no-cors", "referer"=>"https://islandora.traefik.me/", "sec-fetch-site"=>"same-origin", "accept-language"=>"en-GB,en-US;q=0.9,en;q=0.8", "cookie"=>"SSESS702e8d6cb0802797125340f74b95b194=bmn46qr9a1abOHJB49MaVh11ZFWsx7FkTi2nYTYIzQcVXWJI; _pk_ses.1.7058=1; _pk_id.1.7058=2a77528efbcd7a64.1634753158.6.1639665637.1639663840.", "x-forwarded-proto"=>"https", "x-forwarded-port"=>"443", "x-forwarded-for"=>"172.27.0.3", "accept"=>"image/avif,image/webp,image/apng,image/svg+xml,image/*,*/*;q=0.8", "x-real-ip"=>"172.27.0.1", "sec-ch-ua"=>"\" Not A;Brand\";v=\"99\", \"Chromium\";v=\"96\", \"Google Chrome\";v=\"96\"", "sec-ch-ua-mobile"=>"?0", "x-forwarded-server"=>"79fc94af6ba2", "x-forwarded-host"=>"islandora.traefik.me", "sec-ch-ua-platform"=>"\"Linux\"", "host"=>"islandora.traefik.me", "connection"=>"close", "accept-encoding"=>"gzip, deflate, br", "user-agent"=>"Mozilla/5.0 (X11; Linux x86_64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/96.0.4664.93 Safari/537.36", "sec-fetch-dest"=>"image"}} for args: (none) in 9 msec