feat: add github authentication provider

[jrichter1]

Adds github authentication option using an OAuth app to be able to do the following without any extra configuration

await rhdh.configure({ auth: "github" });
await rhdh.deploy();
await loginHelper.loginAsGithubUser();

• oauth for authentication, github app as integration provider in the app config
• app secrets are pulled from the global workspace in vault (the apps should be shareable between workspaces)
• default user credentials also pulled directly from vault unless configured manually
• enables github catalog plugins