feat: Implement webhooks library and perform webhook call on project event

[shydefoo]

Description

• This PR introduces a new webhooks package. The package is meant to be used across caraml components (e.g. merlin, turing, mlp) to call webhooks when specific events occur.
• The package contains the webhook client implementation and abstracts the logic from the user. It provides some helper functions for the user to call in their code when specific events occur.
• The payload to the webhook server and the response can be arbitrary, and it is up to the user to choose what payload to send to the webhook server(s), but only 1 response will be used in the callback
• The response from the webhook is also arbitrary, and it is the responsibility of the component to define/validate the structure of the response from the webhook.
• See the package readme for a detailed explanation of how the webhooks can be configured.

How to use?

1. In the caller package (eg, mlp, merlin), define the list of events that requires webhooks. For example:

const (
	ProjectCreatedEvent wh.EventType = "OnProjectCreated"
	ProjectUpdatedEvent wh.EventType = "OnProjectUpdated"
)

var EventList = []wh.EventType{
	ProjectCreatedEvent,
	ProjectUpdatedEvent,
}

2. Define the event to webhook configuration. Optionally, the configuration can be provided in a yaml file and parsed via the Config struct. In the config file, define the event to webhook mapping for those events as required. For example, if projects need extra labels from an external source, we define the webhook config for the OnProjectCreated event

webhooks:
  enabled: true
  config:
    OnProjectCreated:
      - url: http://localhost:8081/project_created
        method: POST
        onError: abort
        finalResponse: true

3. Call InitializeWebhooks() to get a WebhookManager instance.
   This method will initialize the webhook clients for each event type based on the mapping provided

projectsWebhookManager, err := webhooks.InitializeWebhooks(cfg.Webhooks, service.EventList)

4. Call InvokeWebhooks() method in the caller code based on the event. For a more complete example, see here

---

Project Service changes

• This PR contains 1 example showing how the webhook package can be used when a project is created
• If there are subsequent steps to take, for example labels to add on the project, the webhook is invoked
• A callback is passed to the webhook package to save the updated project data in the database.

Note for reviewers

• More unit tests will be added after 1st round of discussion

[shydefoo]

@leonlnj thanks for the feedback, have addressed most of the changes, lmk what you think. Thanks!

[leonlnj]

thanks, looks much better (at least for me) now!

[deadlycoconuts]

Thanks for the new series of changes! 🚀 LGTM!

[deadlycoconuts]

Ooops wait wait, there's one last thing - can you add the webhook calls to the UpdateProject service method? I think I mentioned this here but you might've left it out.

[shydefoo]

Ooops wait wait, there's one last thing - can you add the webhook calls to the UpdateProject service method? I think I mentioned this here but you might've left it out.

@deadlycoconuts added

[shydefoo]

Merging this now, thanks for the review @leonlnj and @deadlycoconuts