Give user feedback when API-related error occurs

[mnalis]

What is the user problem or growth opportunity you want to see solved?

The user is currently left utterly confused by insufficient error handling.

I.e. when API returns an error, instead of showing the user error, the app just continue showing a progress indicator spinner which never ends, giving user the impression that the app is doing something, when in fact it has encountered an error and is unable to proceed. Thus users waste time waiting for it to finish (which it never will) until they give up.

When API call fails with error, error should be shown to user:

• either generic one like There was an error returned by the server. Please try again, and if error persists report bug with Settings/Send log file at https://github.com/commons-app/apps-android-commons/issues/new
• or (IMHO better) more informative one passing the actual error reported by API to the user, e.g. Wikimedia API returned error: cirrussearch-backend-error / We could not complete your search due to a temporary problem. Please try again later.

(This issue is requested followup to #5225 (comment). Sorry it took some time to properly report it)

How do you know that this problem exists today? Why is this important?

Well, it was present in 4.1.0, but I have not seen it mentioned in #5225 or changelog comments that it has been solved by now.

It is important because users are valuable, and we don't want to confuse them and waste their time.
It would also help developers in debugging reported issues (i.e. when it is clear from screenshot that the error is server-related, and not a Commons app bug)

Who will benefit from it?

all users of the Commons app that happen to encounter API server error (maybe even other network-related errors?)

Anything else you would like to add?

partially related to #5723