Add deployment_id to deployment payloads (#332819)

What does this MR do?

Implements #332819 (closed):

Include the deployment_id in the webhook payload for deployements.

This will allow users to identify the deployment directly, without going through the deployable object.

I have added necessary assertion to the related spec example to ensure that added deployment_id is deployment.id.

How to setup and validate locally

1. Run a verbose http server, like netcat or Python's http.server:

   > nc -l -p 8080
   # or
   > python -m http.server 8080

2. Create a webhook with http://localhost:8080 URL and Deployment events trigger.
3. Trigger webhook by testing it.
4. Look at the output of the server to see deployment_id.

Does this MR meet the acceptance criteria?

Conformity

• I have included changelog trailers, or none are needed. (Does this MR need a changelog?)
• I have added/updated documentation, or it's not needed. (Is documentation required?)
• I have properly separated EE content from FOSS, or this MR is FOSS only. (Where should EE code go?)
• I have added information for database reviewers in the MR description, or it's not needed. (Does this MR have database related changes?)
• I have self-reviewed this MR per code review guidelines.
• This MR does not harm performance, or I have asked a reviewer to help assess the performance impact. (Merge request performance guidelines)
• I have followed the style guides.
• This change is backwards compatible across updates, or this does not apply.

Availability and Testing

• I have added/updated tests following the Testing Guide, or it's not needed. (Consider all test levels. See the Test Planning Process.)
• I have tested this MR in all supported browsers, or it's not needed.
• I have informed the Infrastructure department of a default or new setting change per definition of done, or it's not needed.

Related to #332819 (closed)