richdocuments built-in CODE not compatible with CentOS7

[bigio]

Follwow-up from nextcloud/richdocuments#2667 (comment).

On CentOS 7.9 richdocuments built-in CODE doesn't start and an error related to curl is displayed.
Error is:

cURL error 28: Operation timed out after 45000 milliseconds with -1 out of 0 bytes received (see http://curl.haxx.se/libcurl/c/libcurl-errors.html

The issue is that Collabora_Online.AppImage is linked with libstdc++ that contains GLIBCXX_3.4.20 symbol but CentOS 7 only has GLIBCXX_3.4.19 symbols.
If richdocumentscode is not going to be compatible with CentOS 7 and/or other operating systems, a warning should be printed.