Override default host name

[clairernovotny]

We should do something like this by default to "do the right thing." We already hash user id, we should do the same for the roleinstance/name to prevent possible PII in the name.

// override capture of the hostname
// https://github.com/Microsoft/ApplicationInsights-dotnet/blob/80025b5d79cc52485510d422cfa5a0a8159dac83/src/Microsoft.ApplicationInsights/TelemetryClient.cs#L544
 _client.Context.Cloud.RoleInstance = "Git Extensions";
_client.Context.Cloud.RoleName = "Git Extensions";