auth: set helm default role to kubeshark-viewer

Per round-2 permissions clarifications: SSO users whose claim doesn't
match any built-in role and isn't in AUTH_GROUP_MAPPING should fall
back to a read-only baseline instead of strict-deny ("").

defaultRole="" causes the dashboard to 403-storm gated endpoints from
unmatched users; viewer (snapshot:read only) gives them a sensible
read-only UX while still preventing any state change.

config/configStruct.go

@@ -103,6 +103,7 @@ func CreateDefaultConfig() ConfigStruct {
 			},
 			Auth: configStructs.AuthConfig{
 				RolesClaim:   "groups",
+				DefaultRole:  "kubeshark-viewer",
 				GroupMapping: map[string]string{},
 			},
 			EnabledDissectors: []string{

helm-chart/values.yaml

@@ -154,7 +154,7 @@ tap:
     enabled: false
     type: saml
     rolesClaim: groups
-    defaultRole: ""
+    defaultRole: kubeshark-viewer
     groupMapping: {}
     saml:
       idpMetadataUrl: ""