Fix authorization endpoint for Keycloak auth

[holiiveira]

Description Fix Keycloak url conforming to: https://github.com/alerta/alerta/pull/1683

Fixes #570

Changes Include a brief summary of changes...

• change 1
• change 2
• change 3

Screenshots If it's a UI change add screenshots to demonstrate changes.

Checklist

• [x] Pull request is limited to a single purpose
• [x] Code style/formatting is consistent
• [x] All existing tests are passing
• [x] No unnecessary whitespace changes

[netlify[bot]]

❌ Deploy Preview for peaceful-beignet-dcf974 failed.

Name	Link
🔨 Latest commit	7631aabbe6c12f2ba08e7255c1c9ffabd4df8051
🔍 Latest deploy log	https://app.netlify.com/sites/peaceful-beignet-dcf974/deploys/653bc3b2116f0d0008cb70db