[MM-64708] Fix custom data retention policy navigation (#33011)

Fix navigation to custom data retention policy form by correcting permission
checking functions. The routes for creating and editing custom data retention
policies were using userHasReadPermissionOnSomeResources() with a single
string resource key, causing permission checks to fail and routes to be
hidden.

Changed both custom_policy_form and custom_policy_form_edit routes to use
userHasReadPermissionOnResource() instead, making them consistent with
other working data retention routes.

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-authored-by: Claude <noreply@anthropic.com>

webapp/channels/src/components/admin_console/admin_definition.tsx

@@ -5449,7 +5449,7 @@ const AdminDefinition: AdminDefinitionType = {
                 url: `compliance/data_retention_settings/custom_policy/:policy_id(${ID_PATH_PATTERN})`,
                 isHidden: it.any(
                     it.not(it.licensedForFeature('DataRetention')),
-                    it.not(it.userHasReadPermissionOnSomeResources(RESOURCE_KEYS.COMPLIANCE.DATA_RETENTION_POLICY)),
+                    it.not(it.userHasReadPermissionOnResource(RESOURCE_KEYS.COMPLIANCE.DATA_RETENTION_POLICY)),
                 ),
                 isDisabled: it.not(it.userHasWritePermissionOnResource(RESOURCE_KEYS.COMPLIANCE.DATA_RETENTION_POLICY)),
                 schema: {
@@ -5462,7 +5462,7 @@ const AdminDefinition: AdminDefinitionType = {
                 url: 'compliance/data_retention_settings/custom_policy',
                 isHidden: it.any(
                     it.not(it.licensedForFeature('DataRetention')),
-                    it.not(it.userHasReadPermissionOnSomeResources(RESOURCE_KEYS.COMPLIANCE.DATA_RETENTION_POLICY)),
+                    it.not(it.userHasReadPermissionOnResource(RESOURCE_KEYS.COMPLIANCE.DATA_RETENTION_POLICY)),
                 ),
                 isDisabled: it.not(it.userHasWritePermissionOnResource(RESOURCE_KEYS.COMPLIANCE.DATA_RETENTION_POLICY)),
                 schema: {