Switch to dapr list to obtain running Dapr applications

[philliphoff]

Currently the extension periodically polls all processes to find running Dapr applications (filtering for those. Originally this was necessary because the extension started daprd processes itself (as the only way then to start the sidecar independent of the application being debugged)and dapr list didn't yet exist or, even when it did, would only report processes started via dapr. All of this is no longer necessary; the extension now (by default) uses dapr to start the sidecar and dapr list also is better at listing independent daprd instances.

The extension should now use dapr list to obtain running Dapr applications and dispense with process polling (and it's quirks across platforms).