doc: structural review

- user-guide review.
- add DataDog and StatD configuration.
- sync sample.toml and doc.
- split entry points doc.
- Deprecated.

docs/configuration/backends/eureka.md

@@ -0,0 +1,34 @@
+# Eureka Backend
+
+Træfik can be configured to use Eureka as a backend configuration:
+
+```toml
+################################################################
+# Eureka configuration backend
+################################################################
+
+# Enable Eureka configuration backend
+[eureka]
+
+# Eureka server endpoint.
+# endpoint := "http://my.eureka.server/eureka"
+#
+# Required
+#
+endpoint = "http://my.eureka.server/eureka"
+
+# Override default configuration time between refresh
+#
+# Optional
+# default 30s
+delay = "1m"
+
+# Override default configuration template. For advanced users :)
+#
+# Optional
+#
+# filename = "eureka.tmpl"
+```
+
+Please refer to the [Key Value storage structure](/user-guide/kv-config/#key-value-storage-structure) section to get documentation on traefik KV structure.
+