Search/Autocomplete in Package Configuration Page

[christophenne]

Is your feature request related to a problem? Please describe.
On the package configuration page, the user can enter reference values (ConfigMap, Secret, Package Config), but the input fields are classic text fields without any additional support to show which options there are.

Describe the solution you'd like
For ConfigMap and Secret inputs, the namespace field should show the namespaces of the cluster, and if a namespace has been entered, the name field should show the config maps of this namespace. If possible, once the namespace + name have been entered, the key field shows the possible keys to select from.

For Package inputs, the package field should show all installed packages, and if a package has been selected, the value field should show the possible values.

All of the inputs should support having just plain text too (i.e. none of the available options): Even if we don't allow users to input non-existing objects (to be discussed), someone could always delete some config map or secret afterwards – but the reference should still be visible in the UI.

Describe alternatives you've considered
Classic select without text input field – easier to implement but more difficult for the user if there are a lot of items. Also has the downside that it cannot display broken references (e.g. a reference that has become invalid because a referred config map was deleted).

Additional context
Follow-Up of #121

The most basic way to do this would be an html datalist element, which has text filtering on statically defined options out of the box. But there are certainly more advanced ways to implement this too.