Update the developer docs about feature flags

For the new --random parameter in ChatOps

.gitlab/issue_templates/Feature Flag Roll Out.md

@@ -100,7 +100,7 @@ For visibility, all `/chatops` commands that target production should be execute
   - If the feature flag in code has [an actor](https://docs.gitlab.com/ee/development/feature_flags/#feature-actors), perform **actor-based** rollout.
     - [ ] `/chatops run feature set <feature-flag-name> <rollout-percentage> --actors`
   - If the feature flag in code does **NOT** have [an actor](https://docs.gitlab.com/ee/development/feature_flags/#feature-actors), perform time-based rollout (**random** rollout).
-    - [ ] `/chatops run feature set <feature-flag-name> <rollout-percentage>`
+    - [ ] `/chatops run feature set <feature-flag-name> <rollout-percentage> --random`
   - Enable the feature globally on production environment.
     - [ ] `/chatops run feature set <feature-flag-name> true`
 - [ ] Announce on [the feature issue](ISSUE LINK) that the feature has been globally enabled.

doc/development/feature_flags/controls.md

@@ -72,8 +72,8 @@ group.
 To enable a feature for 25% of the time, run the following in Slack:
 
 ```shell
-/chatops run feature set new_navigation_bar 25 --dev
-/chatops run feature set new_navigation_bar 25 --staging
+/chatops run feature set new_navigation_bar 25 --random --dev
+/chatops run feature set new_navigation_bar 25 --random --staging
 ```
 
 ### Enabling a feature for GitLab.com
@@ -121,7 +121,7 @@ command you make so people can understand the change if they need to.
 To enable a feature for 25% of the time, run the following in Slack:
 
 ```shell
-/chatops run feature set new_navigation_bar 25
+/chatops run feature set new_navigation_bar 25 --random
 ```
 
 This sets a feature flag to `true` based on the following formula:

lib/gitlab/experimentation.rb

@@ -10,9 +10,9 @@
 # The experiment is controlled by a Feature Flag (https://docs.gitlab.com/ee/development/feature_flags/controls.html),
 # which is named "#{experiment_key}_experiment_percentage" and *must* be set with a percentage and not be used for other purposes.
 #
-# To enable the experiment for 10% of the users:
+# To enable the experiment for 10% of the time:
 #
-# chatops: `/chatops run feature set experiment_key_experiment_percentage 10`
+# chatops: `/chatops run feature set experiment_key_experiment_percentage 10 --random`
 # console: `Feature.enable_percentage_of_time(:experiment_key_experiment_percentage, 10)`
 #
 # To disable the experiment: