Add docs explaining how to disable SentryNative

### Description

We already have a page explaining how to disable various other integrations here:
https://docs.sentry.io/platforms/dotnet/configuration/disable-integrations/

Just need to add this, along with a blurb explaining what it does:
```xml
<PropertyGroup>
  <SentryNative>false</SentryNative>
</PropertyGroup>
```