DEV: Provide user input to services using params key

Currently in services, we don’t make a distinction between input
parameters, options and dependencies.

This can lead to user input modifying the service behavior, whereas it
was not the developer intention.

This patch addresses the issue by changing how data is provided to
services:
- `params` is now used to hold all data coming from outside (typically
  user input from a controller) and a contract will take its values from
  `params`.
- `options` is a new key to provide options to a service. This typically
  allows changing a service behavior at runtime. It is, of course,
  totally optional.
- `dependencies` is actually anything else provided to the service (like
  `guardian`) and available directly from the context object.

The `service_params` helper in controllers has been updated to reflect
those changes, so most of the existing services didn’t need specific
changes.

The options block has the same DSL as contracts, as it’s also based on
`ActiveModel`. There aren’t any validations, though. Here’s an example:
```ruby
options do
  attribute :allow_changing_hidden, :boolean, default: false
end
```
And here’s an example of how to call a service with the new keys:
```ruby
MyService.call(params: { key1: value1, … }, options: { my_option: true }, guardian:, …)
```

spec/services/experiments/toggle_spec.rb

@@ -1,56 +1,64 @@
 # frozen_string_literal: true
 
 RSpec.describe Experiments::Toggle do
-  subject(:result) { described_class.call(params) }
-
   describe described_class::Contract, type: :model do
-    subject(:contract) { described_class.new }
-
     it { is_expected.to validate_presence_of :setting_name }
   end
 
-  fab!(:admin)
-  let(:params) { { setting_name:, guardian: } }
-  let(:setting_name) { :experimental_form_templates }
-  let(:guardian) { admin.guardian }
+  describe ".call" do
+    subject(:result) { described_class.call(params:, **dependencies) }
 
-  context "when setting_name is blank" do
-    let(:setting_name) { nil }
+    fab!(:admin)
+    let(:params) { { setting_name: } }
+    let(:setting_name) { :experimental_form_templates }
+    let(:dependencies) { { guardian: } }
+    let(:guardian) { admin.guardian }
 
-    it { is_expected.to fail_a_contract }
-  end
+    context "when data is invalid" do
+      let(:setting_name) { nil }
 
-  context "when setting_name is invalid" do
-    let(:setting_name) { "wrong_value" }
-
-    it { is_expected.to fail_a_policy(:setting_is_available) }
-  end
-
-  context "when a non-admin user tries to change a setting" do
-    let(:guardian) { Guardian.new }
-
-    it { is_expected.to fail_a_policy(:current_user_is_admin) }
-  end
-
-  context "when the admin toggles the feature" do
-    it { is_expected.to run_successfully }
-
-    it "enables the specified setting" do
-      expect { result }.to change { SiteSetting.experimental_form_templates }.to(true)
+      it { is_expected.to fail_a_contract }
     end
 
-    it "disables the specified setting" do
-      SiteSetting.experimental_form_templates = true
-      expect { result }.to change { SiteSetting.experimental_form_templates }.to(false)
+    context "when setting_name is invalid" do
+      let(:setting_name) { "wrong_value" }
+
+      it { is_expected.to fail_a_policy(:setting_is_available) }
     end
 
-    it "creates an entry in the staff action logs" do
-      expect { result }.to change {
-        UserHistory.where(
-          action: UserHistory.actions[:change_site_setting],
-          subject: "experimental_form_templates",
-        ).count
-      }.by(1)
+    context "when a non-admin user tries to change a setting" do
+      let(:guardian) { Guardian.new }
+
+      it { is_expected.to fail_a_policy(:current_user_is_admin) }
+    end
+
+    context "when everything's ok" do
+      it { is_expected.to run_successfully }
+
+      context "when the setting is enabled" do
+        before { SiteSetting.experimental_form_templates = true }
+
+        it "disables the specified setting" do
+          expect { result }.to change { SiteSetting.experimental_form_templates }.to(false)
+        end
+      end
+
+      context "when the setting is disabled" do
+        before { SiteSetting.experimental_form_templates = false }
+
+        it "enables the specified setting" do
+          expect { result }.to change { SiteSetting.experimental_form_templates }.to(true)
+        end
+      end
+
+      it "creates an entry in the staff action logs" do
+        expect { result }.to change {
+          UserHistory.where(
+            action: UserHistory.actions[:change_site_setting],
+            subject: "experimental_form_templates",
+          ).count
+        }.by(1)
+      end
     end
   end
 end