feat: custom error pages (401, 503, 404, etc)

[bodom0015]

Problem

It would be nice to use the same styling as the Workbench WebUI to display generic error messages from navigating

For example:

• 401: Unauthorized
• 404: Not found
• 503: Gateway Temporarily Unavailable

Approach

• feat: custom error pages (401, 503, 404, etc)

Combine this with nds-org/workbench-helm-chart#48 and nds-org/workbench-apiserver-python#17

Meant to replace https://github.com/nds-org/workbench-custom-errors with in-platform error message that share the same style

How to Test

1. Checkout and run this branch locally (see workbench-helm-chart)
2. Navigate to https://kubernetes.docker.internal/ (ignore browser certificate warnings)
3. Login/register with Keycloak
   • You should be brought back to the Workbench, now logged in
4. Add an application from the "All Apps"
   • You should be brought to "My Apps" to see your new app
5. Launch the application
   • You should see the application turn green when it is ready
6. Click the link to navigate to your app (ignore browser certificate warnings)
   • You should see the UI for your app load in the browser