chore(server): disable indexer by default (#12710)

<!-- This is an auto-generated comment: release notes by coderabbit.ai -->
## Summary by CodeRabbit

- **Chores**
	- Updated the default setting for the indexer feature to be disabled by default.
	- Added a sample environment variable for enabling the indexer in the example configuration file.
	- Introduced a new environment variable for the indexer in the CI workflow configuration.
- **Tests**
	- Adjusted test configurations to explicitly enable the indexer feature during test execution.
<!-- end of auto-generated comment: release notes by coderabbit.ai -->

.github/workflows/build-test.yml

@@ -20,6 +20,7 @@ env:
   COVERAGE: true
   MACOSX_DEPLOYMENT_TARGET: '10.13'
   DEPLOYMENT_TYPE: affine
+  AFFINE_INDEXER_ENABLED: true
 
 concurrency:
   group: ${{ github.workflow }}-${{ github.ref }}