[Engineering] Switch to dapr dashboard -p 0

[philliphoff]

Currently the extension uses its own means to select a random port on which to open the Dapr dashboard, to avoid issues with the default port being in use. With Dapr 1.10, the dapr dashboard command itself allows selection of a random port (see dapr/cli#1188). We should switch to that feature, which then simplifies extension logic as well as reduces its dependencies (used for port selection).