integrations: Add Thinkst Canary integration.

This commit adds an integration for Thinkst Canaries - physical, VM and
cloud-based canaries for detecting attackers to a network. Thinkst
Canaries can send webhook alerts when canaries have been tripped, and
this integration will post Zulip messages when these webhooks are
received.

Signed-off-by: David Wood <david@davidtw.co>

zerver/lib/integrations.py

@@ -389,6 +389,7 @@ WEBHOOK_INTEGRATIONS: List[WebhookIntegration] = [
     WebhookIntegration('stripe', ['financial'], display_name='Stripe'),
     WebhookIntegration('taiga', ['project-management']),
     WebhookIntegration('teamcity', ['continuous-integration']),
+    WebhookIntegration('thinkst', ['monitoring']),
     WebhookIntegration('transifex', ['misc']),
     WebhookIntegration('travis', ['continuous-integration'], display_name='Travis CI'),
     WebhookIntegration('trello', ['project-management']),
@@ -619,6 +620,7 @@ DOC_SCREENSHOT_CONFIG: Dict[str, List[ScreenshotConfig]] = {
     'stripe': [ScreenshotConfig('charge_succeeded__card.json')],
     'taiga': [ScreenshotConfig('userstory_changed_status.json')],
     'teamcity': [ScreenshotConfig('success.json'), ScreenshotConfig('personal.json', '002.png')],
+    'thinkst': [ScreenshotConfig('canarytoken_real.json')],
     'transifex': [ScreenshotConfig('', extra_params={'project': 'Zulip Mobile',
                                                      'language': 'en',
                                                      'resource': 'file',