Add design doc for collection-level auto compaction switch (#24041)

Signed-off-by: Congqi Xia <congqi.xia@zilliz.com>

docs/design_docs/20230511-collection_level_autocompaction_switch.md

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+# MEP: Add collection level auto compaction config 
+
+Current state: In Progress
+
+ISSUE: [[Enhancement]: Support collection level config to disable auto-compaction #23993](https://github.com/milvus-io/milvus/issues/23993)
+
+Keywords: Collection, Compaction, Config
+
+Released: N/A
+
+## Summary
+
+Compaction has a config item to control whether auto-compaction is enabled or not. This configuration is global and impacts all collections in system.
+
+In some scenarios, we might want to control the granularity of auto-compaction switch so that it could be achieved that:
+
+- Disable auto-compaction during importing data to prevent rebuilt indexes
+- Disable auto-compaction during some test cases to make system behavior stable
+
+## Design
+
+Add collection level attribute, attribute key is "collection.autocompaction.enabled"(see also pkg/common/common.go).
+
+While handling all compaction signal, check collection level configuration:
+
+- If not set, use global auto-compaction setting
+- If config is valid, use collection level setting
+- If config value is invalid, fallback to global setting
+
+
+## How to change this setting
+
+All collection-level attribute could be changed by `AlterCollection` API
+
+## Test Plan
+
+### Unit tests
+
+Add unit tests for collection level auto compaction switch.
+
+### E2E Tests
+
+Change some case to disable collection auto compaction to rectify test case behavior.
+
+### Integration Tests
+
+- Add test to check auto compaction disabled
+ 
+## References
+
+None
+