Added a troubleshooting page for nuget vulnerability warnings

[ferafiks]

Description

A lot of users have been asking for help relating to package vulnerability warnings in the latest release. This is a part of nuget which we don't have control over and that will continue creating confusion between releases in the future. This PR adds a page about it that we can link users to.

[VaclavElias]

We partially have control over it but don't act fast enough. Many NuGet packages can be updated as soon as there is a new version and with the extensive tests we have now, we might be able to test packages updates. The major packages are resolving their vulnerabilities in a few days or weeks.

Yes, there are also some packages which don't get updated anymore e.g. SharpDX.* and so the transitive warnigns will appear. In SharpDX.* case, I believe this dependency will be removed soon.

Also, there were 3 cases where we nicely nudge a maintainer and the update was released on the packages we depend on.

At this time, I believe if the Avalonia packages are updated to 12.0.4 we will get rid of Tmds.DBus.Protocol warning and in a few weeks we can update Microsoft.Build.* to get rid of System.Security.Cryptography.Xml warning. Although Microsoft.Build.* updatese might break something on our side 🙈🙂.