update summary index to show that declarative is deprecated

Author: camilamacedo86

docs/book/src/SUMMARY.md

@@ -121,7 +121,7 @@
       - [go/v3 (Deprecated)](./plugins/go-v3-plugin.md)
       - [go/v4 (Default init scaffold)](./plugins/go-v4-plugin.md)
     - [To add optional features](./plugins/to-add-optional-features.md)
-      - [declarative/v1](./plugins/declarative-v1.md)
+      - [declarative/v1 (Deprecated)](./plugins/declarative-v1.md)
       - [grafana/v1-alpha](./plugins/grafana-v1-alpha.md)
       - [deploy-image/v1-alpha](./plugins/deploy-image-plugin-v1-alpha.md)
     - [To be extended for others tools](./plugins/to-be-extended.md)