Keep supported triggers in sync with the CLI

[gracegoo-stripe]

Right now the supported list of events lives as a static list in our extension:

vscode-stripe/src/commands.ts

Line 26 in e2f8389

supportedEvents: string[] = [

We need a better way to keep this in sync. Couple of options:

1. Make a call to the CLI to grab the list of supported events at extension startup. The help documentation for stripe trigger does spit out the list of events that we can parse, or we can add a special subcommand to triggers to give us this list.
2. Create a build target to update this list.