Dfeshiny update disconnect msg cookies navid

[JT-39]

Pull request overview

Addressing the first checkbox of issue #69 . The corrected {dfeshiny} function custom_disconnect_message() is now reintegrated into the app and my temporary fix function has been removed (``)

Pull request checklist

Please check if your PR fulfills the following:

• Tests for the changes have been added (for bug fixes / features)
• Docs have been reviewed and added / updated if needed (for bug fixes / features)
• Tests have been run locally and are passing (shinytest2::test_app())
• Code is styled according to tidyverse styling (checked locally with styler::style_dir() and lintr::lint_dir())

What is the current behaviour?

The cookies_banner_server_jt() function is a temporary fix while there is a typo in dfeshiny::cookies_banner_server(). However, this has now been fixed.

What is the new behaviour?

See the overview. Closing #69 .

Anything else

Still waiting on {dfeshiny} to add in the option to have both a refresh link to the current bookmarked site and also refresh the site back to its default state. This will address the second checkbox of #69 , which will created as a new issue:

dfe-analytical-services/dfeshiny#80