Remove usage of `Config::Entry::Configurable#helpers` method

What does this MR do?

Related to #208898 (closed)

The DSL to define CI config keywords has an helpers method that defines methods for those entries that are passed in as parameters.

We have noticed that it can get confusing to know what helpers to create. Helpers should only be created for entries and not for attributes of an entry. In !25683 (merged) we fixed the usage.

The current MR instead fixed the usability by completely removing the need to specify helpers and by consequence the chance of defining wrong ones. We do this by automatically define helpers for any entry.

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