Slightly reduce RAM usage (#7301)

* No need to re-require sidekiq plugins, they are required via Gemfile

* Add derailed_benchmarks tool, no need to require TTY gems in Gemfile

* Replace ruby-oembed with FetchOEmbedService

Reduce startup by 45382 allocated objects

* Remove preloaded JSON-LD in favour of caching HTTP responses

Reduce boot RAM by about 6 MiB

* Fix tests

* Fix test suite by stubbing out JSON-LD contexts

Gemfile.lock

@@ -75,6 +75,7 @@ GEM
       aws-sigv4 (~> 1.0)
     aws-sigv4 (1.0.2)
     bcrypt (3.1.11)
+    benchmark-ips (2.7.2)
     better_errors (2.4.0)
       coderay (>= 1.0.0)
       erubi (>= 1.0.0)
@@ -138,6 +139,14 @@ GEM
     css_parser (1.6.0)
       addressable
     debug_inspector (0.0.3)
+    derailed_benchmarks (1.3.4)
+      benchmark-ips (~> 2)
+      get_process_mem (~> 0)
+      heapy (~> 0)
+      memory_profiler (~> 0)
+      rack (>= 1)
+      rake (> 10, < 13)
+      thor (~> 0.19)
     devise (4.4.3)
       bcrypt (~> 3.0)
       orm_adapter (~> 0.1)
@@ -206,6 +215,7 @@ GEM
     fuubar (2.3.1)
       rspec-core (~> 3.0)
       ruby-progressbar (~> 1.4)
+    get_process_mem (0.2.1)
     globalid (0.4.1)
       activesupport (>= 4.2.0)
     goldfinger (2.1.0)
@@ -226,6 +236,7 @@ GEM
       concurrent-ruby (~> 1.0)
     hashdiff (0.3.7)
     hashie (3.5.7)
+    heapy (0.1.3)
     highline (1.7.10)
     hiredis (0.6.1)
     hitimes (1.2.6)
@@ -264,10 +275,6 @@ GEM
     json-ld (2.2.1)
       multi_json (~> 1.12)
       rdf (>= 2.2.8, < 4.0)
-    json-ld-preloaded (2.2.3)
-      json-ld (>= 2.2, < 4.0)
-      multi_json (~> 1.12)
-      rdf (>= 2.2, < 4.0)
     jsonapi-renderer (0.2.0)
     jwt (2.1.0)
     kaminari (1.1.1)
@@ -502,7 +509,6 @@ GEM
       rainbow (>= 2.2.2, < 4.0)
       ruby-progressbar (~> 1.7)
       unicode-display_width (~> 1.0, >= 1.0.1)
-    ruby-oembed (0.12.0)
     ruby-progressbar (1.9.0)
     ruby-saml (1.7.2)
       nokogiri (>= 1.5.10)
@@ -557,6 +563,7 @@ GEM
     sshkit (1.16.0)
       net-scp (>= 1.1.2)
       net-ssh (>= 2.8.0)
+    stackprof (0.2.11)
     statsd-ruby (1.2.1)
     stoplight (2.1.3)
     streamio-ffmpeg (3.0.2)
@@ -645,6 +652,7 @@ DEPENDENCIES
   chewy (~> 5.0)
   cld3 (~> 3.2.0)
   climate_control (~> 0.2)
+  derailed_benchmarks
   devise (~> 4.4)
   devise-two-factor (~> 3.0)
   devise_pam_authenticatable2 (~> 9.1)
@@ -668,7 +676,7 @@ DEPENDENCIES
   i18n-tasks (~> 0.9)
   idn-ruby
   iso-639
-  json-ld-preloaded (~> 2.2)
+  json-ld (~> 2.2)
   kaminari (~> 1.1)
   letter_opener (~> 1.4)
   letter_opener_web (~> 1.3)
@@ -714,7 +722,6 @@ DEPENDENCIES
   rspec-retry (~> 0.5)
   rspec-sidekiq (~> 3.0)
   rubocop (~> 0.55)
-  ruby-oembed (~> 0.12)
   ruby-progressbar (~> 1.4)
   sanitize (~> 4.6)
   scss_lint (~> 0.57)
@@ -726,6 +733,7 @@ DEPENDENCIES
   simple_form (~> 4.0)
   simplecov (~> 0.16)
   sprockets-rails (~> 3.2)
+  stackprof
   stoplight (~> 2.1.3)
   streamio-ffmpeg (~> 3.0)
   strong_migrations (~> 0.2)