feat(deployment): add envFrom support for ConfigMap/Secret environment variables

Add support for loading environment variables from ConfigMap or Secret
resources using envFrom field, following Kubernetes best practices for
configuration management.

Changes:
- Add jellyfin.envFrom parameter in values.yaml
- Add envFrom section in deployment.yaml template (before env)
- Provide comprehensive documentation with examples
- Bump chart version 2.5.0 -> 2.6.0 (minor - new feature)
- Add changelog annotation for Artifact Hub

Use cases:
- Load multiple environment variables from ConfigMap without defining each one
- Load secrets from external secret management systems
- Separate configuration from chart values (12-factor app pattern)
- Simplify configuration for complex deployments

Example usage:
  jellyfin:
    envFrom:
      - configMapRef:
          name: jellyfin-config
      - secretRef:
          name: jellyfin-secrets

Follows standard Kubernetes patterns used by most community Helm charts.

Co-Authored-By: Claude <noreply@anthropic.com>
Signed-off-by: Aleksei Sviridkin <f@lex.la>

charts/jellyfin/templates/deployment.yaml

@@ -59,6 +59,10 @@ spec:
           args:
             {{- toYaml . | nindent 12 }}
           {{- end }}
+          {{- with .Values.jellyfin.envFrom }}
+          envFrom:
+            {{- toYaml . | nindent 12 }}
+          {{- end }}
           {{- with .Values.jellyfin.env }}
           env:
             {{- toYaml . | nindent 12 }}