Fixed unclear login rejection message

[andreas-kupries]

fix #2630

[codecov]

Codecov Report

Attention: 3 lines in your changes are missing coverage. Please review.

Files	Coverage Δ
internal/api/v1/middleware/authentication.go	56.79% <50.00%> (+0.26%)	⬆️

... and 11 files with indirect coverage changes

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[mmartin24]

Checked in

✔️  Epinio Environment
Platform: k3s
Kubernetes Version: v1.26.10+k3s2
Epinio Server Version: v1.11.0-rc1
Epinio Client Version: v1.11.0-rc1
OIDC enabled: true

---

Expected message ok after entering wrong user:

➜  epinio git:(main) ✗ epinio login -u wrong-user https://epinio.192.168.16.3.omg.howdoi.website

🚢  Login to your Epinio cluster [https://epinio.192.168.16.3.omg.howdoi.website]
Password: 

⚠️  Certificate signed by unknown authority

|     KEY     |      VALUE       |
|-------------|------------------|
| Issuer Name | CN=epinio-ca     |
| Common Name | epinio-ca        |
| Expiry      | 2024-February-21 |

Do you want to trust it (y/n): y

✔️  Trusting certificate for address https://epinio.192.168.16.3.omg.howdoi.website...

❌  error verifying credentials: error while connecting to the Epinio server: user not found