feat: add bearer/basic auth support to webhook notifications (#2369)

[jannikbx]

Fixes #2369 - Adds optional authentication to webhook notifications.

Changes

• Added WebhookAuthType (none | basic | bearer) and auth fields to Notification interface
• Added getAuthHeaders() to WebhookProvider for Basic Auth (base64) and Bearer token
• Integrated auth headers into sendMessage() and sendTestAlert()
• Added 4 test cases for auth behavior

How it works

Basic Auth: Notification gets webhookAuthType: "basic", webhookAuthUsername, webhookAuthPassword → sends Authorization: Basic <base64>
Bearer: Notification gets webhookAuthType: "bearer", webhookAuthToken → sends Authorization: Bearer <token>
None: No auth fields → no Authorization header (unchanged behavior)

[jannikbx]

Hey @smz202000, YoinkingFishy mentioned that #3785 and my PR (#3802) are both implementing #2369, so we should probably coordinate before either gets merged.

Quick status check from my side: my PR has all CI checks green and no open review comments so far. Yours still has a few open items – the changes ajhollid requested, and the format checks are still failing.

How do you want to handle this? Either you finish those up on #3785 and we align the field names so yours can get merged, or I adapt my PR to match your naming and add the client-side part. I'm fine with either – just don't want us to block each other.

Let me know what works for you!

[jannikbx]

Hi maintainers! This PR is now complete and ready for review. It implements bearer/basic auth for webhook notifications (#2369).

What's included:

• Server provider (webhook.ts): getAuthHeaders() with switch/case for none / basic / bearer, applied to both sendMessage() and sendTestAlert()
• Persistence (notification.model.ts): 4 new schema fields (webhookAuthType with enum + default none, username, password, token)
• Server validation (notificationValidation.ts): conditional validation via superRefine — basic requires username + password, bearer requires token
• Client UI (create/index.tsx): auth-type selector (none/basic/bearer) with conditional fields, plus updated types, form defaults, client validation, and i18n strings

Happy to adjust based on feedback. Thanks!