feat(plugins/Subscription): Manage GOOSE service connections

[Flurb]

Also adding some tests for the subscription plugin, which were not included in the subscriber-plugin branch.

[Flurb]

Updating an element is done as follows:

private async replaceElement(original: Element, clone: Element) {
    const parent = original.parentElement;

    this.dispatchEvent(
      newActionEvent({
        old: {
          parent: parent!,
          element: original,
          reference: original.nextSibling
        }
      })
    );

    await this.updateComplete;

    this.dispatchEvent(
      newActionEvent({
        new: {
          parent: parent!,
          element: clone,
          reference: clone.nextSibling
        }
      })
    );
  }

I want this to be done with 1 newActionEvent instead of 2, but I can't get it to work.
When I use a new element and an old element as well at the same time, it's just adding the new element into the old element.

It's working as it is now, but it's not a classy solution. You're free to fix it :)
It seems like a bug into the newActionEvent process, but I'm not sure.

[JakobVogelsang]

LGTM