Goal: Enable richer and more secure integration of Quay with other automation systems using webhooks that require authentication.

Why is this important: While Quay features notifications that can call out to external webhooks we do not support any form of authentication. This hinders the ability to use of modern CI/CD systems like Github's repository_dispatch event as a callback to successful builds. The event itself is needed to trigger Github Actions which is similar in nature to other Ci/CD pipelines (Github Actions). People have to build and maintain their own translation layer like this: https://github.com/lewagon/quay-github-actions-dispatch

Acceptance criteria:

• webhook notifications support HTTP basic authentication
• webhook notifications support adding custom HTTP headers
• specifically, webhook notifications allow the use of authentication headers according to RFC 7235
• the headers and HTTP basic auth credentials are stored encrypted in the database
• webhook UI allows to enter the data required for the above