Upgrade to Rails 6

- Added listen gem because rails app:update failed without it
- Removes nsa gem because it requires activesupport < 6
  Oddly, there's a newer version per GitHub that's not on RubyGems
  that raises the requirement to < 7. But, we need a new release
  before we can use that.
- Upgrade rails-i18n to v6, for Rails 6 compatibility
- Remove redis-rails since it requires Rails < 6, but we can just use
  the regular Rails :redis_cache_store that was introduced in 5.2.
- Run `rails app:update`
  - Had to weed through the `config/environments` changes to pick up
    newly added settings, while not losing settings that were
    intentionally configured
  - This generated config/initializers/new_framework_defaults_6_0.rb.
    The goal is to uncomment all of the settings in that file. Once
    they're all uncommented, delete the file and edit
    config/application.rb's load_defaults to be 6.0.
  - force_ssl controller method is deprecated in favor of a Rails
    config setting.
  - bin/setup was generated by Rails
  - Verbose query logging in development is really helpful. It shows
    you what line of code caused a query to execute.
  - Calling establish_connection after worker boot isn't necessary
    with ActiveRecord anymore. ActiveRecord handles it gracefully.
  - Rails generated a migration to add a foreign key for ActiveStorage.
    Gab currently doesn't use ActiveStorage, and instead uses Paperclip
    (since ActiveStorage didn't exist when Mastadon started). So, this
    change isn't relevant to Gab.
- Added ` || ''` in the profiles controller, because I was unable
  to save a change to a newly created profile. (This probably
  explains the 500 error I received on prod Gab recently.)

db/migrate/20210123050026_add_foreign_key_constraint_to_active_storage_attachments_for_blob_id.active_storage.rb

@@ -0,0 +1,10 @@
+# This migration comes from active_storage (originally 20180723000244)
+class AddForeignKeyConstraintToActiveStorageAttachmentsForBlobId < ActiveRecord::Migration[6.0]
+  def up
+    return if foreign_key_exists?(:active_storage_attachments, column: :blob_id)
+
+    if table_exists?(:active_storage_blobs)
+      add_foreign_key :active_storage_attachments, :active_storage_blobs, column: :blob_id
+    end
+  end
+end

db/schema.rb

@@ -2,15 +2,15 @@
 # of editing this file, please use the migrations feature of Active Record to
 # incrementally modify your database, and then regenerate this schema definition.
 #
-# Note that this schema.rb definition is the authoritative source for your
-# database schema. If you need to create the application database on another
-# system, you should be using db:schema:load, not running all the migrations
-# from scratch. The latter is a flawed and unsustainable approach (the more migrations
-# you'll amass, the slower it'll run and the greater likelihood for issues).
+# This file is the source Rails uses to define your schema when running `rails
+# db:schema:load`. When creating a new database, `rails db:schema:load` tends to
+# be faster and is potentially less error prone than running all of your
+# migrations from scratch. Old migrations may fail to apply correctly if those
+# migrations use external dependencies or application code.
 #
 # It's strongly recommended that you check this file into your version control system.
 
-ActiveRecord::Schema.define(version: 2021_01_17_210100) do
+ActiveRecord::Schema.define(version: 2021_01_23_050026) do
 
   # These are extensions that must be enabled in order to support this database
   enable_extension "plpgsql"