Fixes for wizard when in edit mode

Description

Fixes #180.

disable Next button when a configuration will be fed to the wizard (edit or from another cluster)
add loading to the wizard when editing a cluster

Edit a cluster locally, spinner is shown instead of the wizard while loading the config
From another cluster works just as before, but with the Next button disabled while loading the config

[x] I added tests to new or existing code
[ ] I removed hardcoded strings and used react-i18next library (useTranslation hook and/or Trans component), see an example here
[ ] I made sure no sensitive info gets logged at any time in the codebase (see here) (e.g. no user info or details, no stacktraces, etc.)
[ ] I made sure that any GitHub issue solved by this PR is correctly linked
[ ] I checked that infrastructure/update_infrastructure.sh runs without any error
[ ] I checked that npm run build builds without any error
[ ] I checked that clusters are listed correctly
[x] I checked that a new cluster can be created (config is produced and dry run passes)
[ ] I checked that login and logout work as expected

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