Description:

When to use the donet tool(confluent.apache.avro.avrogen), got the following error:

A fatal error occurred, the required library libhostfxr.so could not be found.
If this is a self-contained application, that library should exist in [/home/$username$/.dotnet/tools/.store/confluent.apache.avro.avrogen/1.7.7.5/confluent.apache.avro.avrogen/1.7.7.5/tools/netcoreapp2.1/any/].
If this is a framework-dependent application, install the runtime in the default location [/usr/share/dotnet] or use the DOTNET_ROOT environment variable to specify the runtime location.

I find the DOTNET_ROOT environment variable in the /usr/bin/dotnet as following:

```
export DOTNET_ROOT=/opt/dotnet
exec /opt/dotnet/dotnet "$@"
```

But this DOTNET_ROOT environment variable is not global, so when I use the dotnet tool, there is no such an environment variable.

Additional info:
* package version(s)
* config and/or log files etc.
* link to upstream bug report, if any

Steps to reproduce:
dotnet tool install -g Confluent.Apache.Avro.AvroGen
avrogen -s my_schema.asvc .