Unify notifications

[steffinchen]

Summary

Makes the notification behavior consistent.

Closes https://github.com/appuio/cloud-portal/issues/542

Details

• All error toast messages are sticky, so the user has enough time to read / screenshot them
• Slightly changed wording of error message, so they are not too technical, and if relevant, gives the user a hint what they can do to resolve it (e.g. enable local storage)
• No technical error details (such as urls, port) are shown to the user
• All toasts can be dismissed by the user
• Success messages disappear automatically (i.e. disappear automatically after a few seconds)

Checklist

• [x] Categorize the PR by setting a good title and adding one of the labels: bug, enhancement, documentation, change, breaking, as they show up in the changelog
• [x] Update tests.
• [x] Link this PR to related issues.

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App URL	https://portal-pr-554-appuio-control-api-preview.apps.cloudscale-lpg-2.appuio.cloud
Revision	f87a7bb71afe1d4b27716d9e16c4fb5f681f9156
Helm release	appuio-control-api-preview/portal-pr-554
Cluster	https://api.cloudscale-lpg-2.appuio.cloud:6443

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🚀 Preview deployment active

App URL	https://portal-pr-554-appuio-control-api-preview.apps.cloudscale-lpg-2.appuio.cloud
Revision	91e230a1a82474e73a867005b1ad74ca1eaecf37
Helm release	appuio-control-api-preview/portal-pr-554
Cluster	https://api.cloudscale-lpg-2.appuio.cloud:6443

To uninstall this deployment, close or merge this PR.

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✔️ Preview deployment uninstalled

Helm release	appuio-control-api-preview/portal-pr-554
Cluster	https://api.cloudscale-lpg-2.appuio.cloud:6443