It's insanely hard to install a user certificate on Android 11

[ameshkov]

The old installation intent does not work anymore. Moreover, manual installation does not work either (because of some storage permissions I guess).

Here's what we should do in v3.4:

1. We should not use the default installation approach anymore (gray out the "install automatically" button on Android 11).
2. When the user clicks "Install manually" we should show a detailed explanation of what's going on and warn the user there, that installing a cert will be rather difficult.
3. Step 1: Use ACTION_CREATE_DOCUMENT so that the user could save the certificate to the disk.
4. Step 2: Once it's done, show another dialog explaining the next steps: Open security settings --> scroll down to "Encryption & credentials" --> Choose "Install a certificate" there --> Find the cert that you've just installed.

In the future versions, we should not make stress on HTTPS filtering anymore, it's just too hard for a casual user to install it.