Implement the OCI registry update functionality

[thepetk]

/kind task

Which area/kind this issue is related to?

/area registry

Issue Description

The OCI registry should be up-to-date with the main branch of the provided env var registry repo URL. As a result, a task should be able to update the OCI registry artifacts whenever a trigger is sent to the webhook of the index/server.

The task should receive information about the:

• commit_hash of the latest commit that we are updating the OCI registry.
• the list of affected stacks that the task should look to update.

The task should update the content of the artifacts for the affected stacks and regenerate the index.json (with the new commit_hash inside).

Finally, a new endpoint should be created inside the index/server. This endpoint should only interact with github repo and trigger every new update of the oci-registry artifacts. Note that this endpoint should have an authentication method in order to be sure that the only requester will be the github repo.

Acceptance Criteria

• Add functionality to be able to update specific artifacts inside the oci-registry,
• An endpoint exists so we can receive webhooks from github regarding any updates of the stacks.
• The endpoint is reachable only if the related env var (see Add support for registryRepoURL env var to the registry deployment. #1507) is set.

[thepetk]

Note the webhook on the index/server should be able to support two types of triggers from github:

1. Github sends a simple trigger to the webhook after a github event. The index/server checks the updated code for any affected stacks.
2. Github sends a trigger with information about affected stack (need to decide the format) so index/server updates directly the given updated stacks.