Set feature flag forward_npm_package_registry_requests enabled by default

What does this MR do?

Set the feature flag forward_npm_package_registry_requests enabled by default.

This feature flag controls if GitLab will forward NPM package requests to npmjs.org or not when an NPM package doesn't exist within the GitLab NPM repository.

Note that this feature is also controlled by an Application Setting. See the documentation MR: !26888 (merged)

See the relevant issue: #55344 (closed)

See the rollout issue: #209886 (closed)

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry
• Documentation (if required)
• Code review guidelines
• Merge request performance guidelines
• Style guides
• Database guides
• Separation of EE specific content

Availability and Testing

• Review and add/update tests for this feature/bug. Consider all test levels. See the Test Planning Process.
• Tested in all supported browsers
• Informed Infrastructure department of a default or new setting change, if applicable per definition of done

Security

If this MR contains changes to processing or storing of credentials or tokens, authorization and authentication methods and other items described in the security review guidelines:

• Label as security and @ mention @gitlab-com/gl-security/appsec
• The MR includes necessary changes to maintain consistency between UI, API, email, or other methods
• Security reports checked/validated by a reviewer from the AppSec team