Add support for Webhooks in Ansible-Semaphore

This MR adds support for Webhooks to trigger Ansible Templates and run Playbooks based on configuration given to a webhook that can be potentially received by semaphore.

Webhook Configuration

The change hereby presented adds a new item on the sidebar titled Webhooks, navigating here will present the user with a list of Webhooks being recognized by the system.

A webhook links to a template in Semaphore which will be run when the e webhook satisfied its extractor configuration and has succeeded all Matcher criteria.

Webhook Extractors

A webhook consists of 1 or more Webhook Extractors which in turn have 1 or more Matchers and Extracted Values

Webhook Matchers

A Matcher defines a characteristic of the webhook event being sent to the semaphore system where the system will read the request for its body or header data and match on fields presented in the webhook.

Consider the following Webhook posted to semaphore system:

POST /webhook HTTP/1.1
Host: semaphore.example.org
Content-Type: application/x-application-json

{
  "data": {
    "field1": "a",
    "field2": "b"
  }
}

A matcher may now select to parse the body JSON to retrieve for example data.field1
It may now try to :

• test if a field value is equal
• test if a field value is unequal
• test if a field value contains a string

If all the Matchers for an extractor have been met the system will engage the extractor linked Webhook Extract Values

Extracted Value

An extracted value is any field selected from the webhook to turn into a variable on the template fields/values being passed to the playbook being run as part of the template attached to the webhook object.

Considering the previously described Webhook posted to semaphore system:

POST /webhook HTTP/1.1
Host: semaphore.example.org
Content-Type: application/x-application-json

{
  "data": {
    "field1": "a",
    "field2": "b"
  }
}

The extractvalue may now select data.field2 and assign it to VARIABLE_A which would be passed as configuration variable to the ansible-playbook run invoked by the template.

This way the system can augment the received data to provide it to the playbook being run.

Webhook execution

Upon receiving a Webhook that satisfied all matchers and has successfully extracted all the required values into variables, the system will attempt to trigger a run of a template, build or deployment.