Remove unnecessary assets from sprockets precompile

What does this MR do?

sprocket-rails adds some precompile assets we actually do not need.

It copies all non js and CSS files from the app/assets/ older.

In our case this copies for example: Vue, Markdown and Graphql, which we do not need for production.

We remove this default behavior and then reimplement it in order to consider ee/ as well and remove those other files we do not need.

For reference: https://github.com/rails/sprockets-rails/blob/v3.2.1/lib/sprockets/railtie.rb#L84-L87

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