Make ICSx5 work with ics files offered as attachments from webpages

[devvv4ever]

Some websites may provide ics calendars not as a direct link or redirection, but as an attachment.

We should consider this use case also. For example if users enter a link to a html page in ICSx5 (see below) the web page could offer the ics as an attachment like seen here:

https://www.tanzschule-beier.de/cms/events-abonnieren/ical/3/title/Veranstaltungen%2Bf%25C3%25BCr%2BSch%25C3%25BCler%2Bund%2BJugendliche.html

The web server answers with:

GET /cms/events-abonnieren/ical/3/title/Veranstaltungen%2Bf%25C3%25BCr%2BSch%25C3%25BCler%2Bund%2BJugendliche.html HTTP/2

...

< HTTP/2 200
< expires: Thu, 19 Nov 1981 08:52:00 GMT
< pragma: no-cache
< content-disposition: attachment; filename="20221221124752.ics"
< cache-control: max-age=10
< set-cookie: PHPSESSID=tj47g1vtddht4dpcqfqquiml52; path=/cms; HttpOnly
< content-length: 5536
< content-type: text/calendar; charset=utf-8
< date: Wed, 21 Dec 2022 11:47:52 GMT
< server: Apache (custom)

... after that the VCALENDAR data follows ...

If it is possible we should discuss whether this can/should be supported by ICSx5.

[devvv4ever]

Seems that this was caused due to automatic blocking okhttp via the user agent to avoid automatic grabbing. Can only be fixed on the web server.