Fix support for ETW tracing on linux and custom backends

[sebastianburckhardt]

Description

There's a bug in the linux trace collection which means ETW event sources inside custom backends are not collected.

The problem is in EventSourceListener.cs. Specifically, OnEventSourceCreated is called before the constructor EventSourceListener is called, thus the field durabilityProviderEventSourceName has not been initialized yet. So the comparison always fails.

[ConnorMcMahon]

@bachuv, I believe this is related to your recent change. We will want to make sure we fix this before we have a bundles release that could break linux logging for existing Linux consumption customers.

[bachuv]

@ConnorMcMahon It looks like there is a delay for when durabilityProviderEventSourceName gets assigned so any calls to OnEventSourceCreated before that will evaluate eventSource.Name == this.durabilityProviderEventSourceName as false. Before updating this condition to use durabilityProviderEventSourceName, there were comparisons between eventSource.Name and hard coded event source name values (e.g. "DurableTask-AzureStorage"). The reason we added this field was to support a variety of durability providers and allow customers to configure their own durability provider. Maybe we go back to having a list of hard coded values for supported durability providers and if a customer uses another durability provider then they set an additional environment variable with the event source name?