SlackProvider implements SlackTransport via a Slack incoming webhook URL.
SlackProvider(options: SlackProviderOptions)
Creates a SlackProvider.
Parameters
options: SlackProviderOptions
Provider configuration
send(message: SlackMessage): Promise<void>
Posts a message to the Slack webhook.
Slack signals success only when HTTP 200 AND body is the literal "ok" —
a compound check: !response.ok or response.text !== 'ok' each
constitute failure arms.