[TaskProcessing] Add support for webhooks

[julien-nc]

• 2 new columns/attributes for tasks: webhookUri and webhookMethod
• When a task finishes (is canceled, fails or succeeds), we try to "run" the webhook
• If the method is "HTTP:GET", "HTTP:POST"... we make a simple HTTP request
• If the method is "AppAPI:APP_ID:HTTP_METHOD" we directly send a request to the exApp
• The request body contains the task ID and status

Questions:

• Do we want to combine so much information in the method column/attr?
• What do we want to include in the request body/headers?

[bigcat88]

LGTM

[provokateurin]

I'm not sure I understand the purpose of these changes. Is this part of the new webhook stuff or specific to task processing api? If it is the former then it seems wrong to me to implement it in the task processing api? Maybe I'm missing something though.

[julien-nc]

It seems like the 3rd party repo is not up to date in master. The Block merging with outdated 3rdparty action will be fixed when someone pushes the new subproject commit hash.

I don't really get why the OpenAPI action is failing though.

[provokateurin]

The OpenAPI failure is random, it seems to happen once in a while without an apparent reason.

[julien-nc]

@provokateurin If we think about the workflow engine, it would indeed be possible in a flow to:

• schedule a task, get its ID
• run an custom approval script to block the flow execution
• in the approval script, register a webhook for the "task finished" event with a filter on the task ID, setting the target URI to the resume endpoint of the approval script
• after the approval step is resumed, run a script that unregisters the webhook because we don't need it anymore

But it is way more simple to:

• run an approval script
• schedule a task in the approval script and tell the task processing API to call the resume endpoint when the task has finished

Having the webhook_listeners app does not prevent us from implementing webhook-like features in other places where it's convenient. That's the reasoning behind this PR.