Enable Generic packages by default

Enable `generic_packages` feature flag by default and update the
corresponding section in the documentation.

Rollout issue https://gitlab.com/gitlab-org/gitlab/-/issues/239133.

Related to https://gitlab.com/groups/gitlab-org/-/epics/4209.

changelogs/unreleased/generic-packages-enable-by-default.yml

+---
+title: Add support for Generic packages
+merge_request: 45102
+author:
+type: added

config/feature_flags/development/generic_packages.yml

@@ -4,4 +4,4 @@ introduced_by_url: https://gitlab.com/gitlab-org/gitlab/-/merge_requests/40045
 rollout_issue_url: https://gitlab.com/gitlab-org/gitlab/-/issues/239133
 group: group::release management
 type: development
-default_enabled: false
+default_enabled: true

doc/user/packages/generic_packages/index.md

@@ -7,11 +7,11 @@ info: To determine the technical writer assigned to the Stage/Group associated w
 # GitLab Generic Packages Repository **(CORE)**
 
 > - [Introduced](https://gitlab.com/groups/gitlab-org/-/epics/4209) in GitLab 13.5.
-> - It's [deployed behind a feature flag](../../../user/feature_flags.md), disabled by default.
-> - It's disabled on GitLab.com.
+> - It's [deployed behind a feature flag](../../../user/feature_flags.md), enabled by default.
+> - It's enabled on GitLab.com.
 > - It's able to be enabled or disabled per-project.
-> - It's not recommended for production use.
-> - To use it in GitLab self-managed instances, ask a GitLab administrator to [enable it](#enable-or-disable-generic-packages-in-the-package-registry).
+> - It's recommended for production use.
+> - For GitLab self-managed instances, GitLab administrators can opt to [disable it](#enable-or-disable-generic-packages-in-the-package-registry).
 
 CAUTION: **Warning:**
 This feature might not be available to you. Check the **version history** note above for details.
@@ -115,10 +115,10 @@ download:
 
 ### Enable or disable generic packages in the Package Registry
 
-Support for generic packages is under development and not ready for production use. It is
-deployed behind a feature flag that is **disabled by default**.
+Support for generic packages is under development but ready for production use.
+It is deployed behind a feature flag that is **enabled by default**.
 [GitLab administrators with access to the GitLab Rails console](../../../administration/feature_flags.md)
-can enable it.
+can opt to disable it.
 
 To enable it:
 

lib/api/generic_packages.rb

@@ -101,7 +101,7 @@ module API
       include ::API::Helpers::Packages::BasicAuthHelpers
 
       def require_generic_packages_available!
-        not_found! unless Feature.enabled?(:generic_packages, project)
+        not_found! unless Feature.enabled?(:generic_packages, project, default_enabled: true)
       end
 
       def project