Clear modal notifs when opening modal

[Arnei]

When opening a modal, modal notifications were not properly cleared. This would lead to notifications being displayed in the wrong modals, i.e. "This event cannot be edited due to an active workflow" would appear on a create series modal. This patch should fix that.

Includes #1021.

How to test this

Can be tested as usual. Trigger a warning in one modal and check if it appears in different modals.

[github-actions]

Use docker or podman to test this pull request locally.

Run test server using develop.opencast.org as backend:

podman run --rm -it -p 127.0.0.1:3000:3000 ghcr.io/opencast/opencast-admin-interface:pr-1051

Specify a different backend like stable.opencast.org:

podman run --rm -it -p 127.0.0.1:3000:3000 -e PROXY_TARGET=https://stable.opencast.org ghcr.io/opencast/opencast-admin-interface:pr-1051

It may take a few seconds for the interface to spin up.
It will then be available at http://127.0.0.1:3000.
For more options you can pass on to the proxy, take a look at the README.md.

[github-actions]

This pull request is deployed at test.admin-interface.opencast.org/1051/2025-01-31_14-08-50/ .
It might take a few minutes for it to become available.

[github-actions]

This pull request has conflicts ☹
Please resolve those so we can review the pull request.
Thanks.

[github-actions]

This pull request has conflicts ☹
Please resolve those so we can review the pull request.
Thanks.

[github-actions]

This pull request has conflicts ☹
Please resolve those so we can review the pull request.
Thanks.

[github-actions]

This pull request has conflicts ☹
Please resolve those so we can review the pull request.
Thanks.

[owi92]

This does what is described. Since #1021 is included here, my comment from there regarding the Tobira notif applies to this as well.
I suppose that other PR can be closed. It's up to you whether you want to remove the empty then()s here as well.