Adjust display of error messages in TableCellLink for improved usability

Adjust this code in loadResultsForProvider(providerId, term) in TableCellLink.vue:

let res = null
	try {
		res = await axios.get(generateOcsUrl('/search/providers/' + providerId + '/search?term=' + term))
	} catch (e) {
		displayError(e, t('tables', 'Could not load link provider results.'))
		this.setProviderLoading(providerId, false)
		return
	}

consider combining errors from multiple providers—right now each failure (like network issues or provider unavailability) pops up its own message, which could get a bit much for users. A single, combined error might feel smoother

Originally posted by @silverkszlo in https://github.com/nextcloud/tables/pull/1977#discussion_r2276855635

Yeah, makes sense. And right now that I have added the link validation, trying to save several times by hitting enter multiple times with an invalid link leads to multiple popups with the same message. Could be improved for sure

Originally posted by @enjeck in https://github.com/nextcloud/tables/pull/1977#discussion_r2280971961

Start in TableCellLink.vue at loadResultsForProvider(providerId, term), especially the axios request and displayError call. Trace how multiple provider failures and repeated invalid-link saves surface messages, then verify that related errors are presented together or without duplicate popups.