Cleanup useMutation messages

[mlqn]

We are currently using different components to display messages, which leads to some visual inconsistencies.
I suggest replacing them with the new toast component and removing error messages that are duplicates of the default error message.

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Generating data model

1. Go to Datamodell
2. Add an empty object
3. Click Generer modeller
4. The Request failed with status code 500 error message should not be displayed

datamodel-error.mov

1. Go toDatamodell
2. Create a new data model
3. Click Generer modeller
4. The success message should be displayed as a toast to be consistent with the other success messages

datamodel-success.mov

Committing and pushing changes

1. Add a new component into the layout
2. Add a new file in Gitea
3. Click Last opp dine endringer, add a commit message, and click Valider endringer
4. The popover should not show a success message when an error occurs

commit-and-push-error.mov

Creating a new app

1. Go to Dashboard
2. Click Opprett ny applikasjon
3. Write an app name that already exists
4. Det har oppstått en feil error message should not be displayed

create-existing-app.mov

1. Go to Dashboard
2. Click Opprett ny applikasjon
3. Block the /create-app endpoint using a tool like Requestly
4. Noe gikk galt ved oppretting av appen should not be displayed as it is a duplicate of the default error message

create-app-error.mov

Deleting/Editing a text resource

1. Go to Tekst
2. Block the /text/keys endpoint using Requestly
3. Delete or edit a text
4. The javascript alert should not be displayed as it is a duplicate of the default error message

text-error.mov

Resetting changes

1. Go to Oversikt
2. Click Slett mine endringer
3. Write the current application name and click Slett mine endringer
4. The popover is buggy and should be replaced by toast for error and success messages

reset-changes-success.mov

Building an app

1. Go to Deploy
2. Block the /releases and /deployments endpoints using Requestly
3. Write a version number, a description and click Bygg versjon
4. This popover should not be displayed as it is a duplicate of the default error message

[JamalAlabdullah]

I tested, It works well 👍