Merge pull request #87 from Azure/u/visanka/UpdateDocs

Updated docs with build v1.0.0-preview-008920001-990

releaseNotes/MicrosoftExtensionsConfigurationAzureAppConfiguration.md

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+## Microsoft Extensions Azure App Configuration
+
+### v1.0.0-preview-008920001-990
+
+* Added `TrimKeyPrefix` method to remove prefixes from the list of returned key-values from the config store.
+* Improved durability on Watch, so that transient network errors do not cause the process to detach.
+* Added additional retries on network error when using `ConnectWithManagedIdentity`.
+* Enabled Correlation-Context for telemetry/request-tracing.
+    * ***Telemetry can be disabled by setting the environment variable `AZURE_APP_CONFIGURATION_TRACING_DISABLED` to `True` or `1`***
+    * Added telemetry for the following:
+        * Hosting platform.
+        * Differentiating Initialization and Watch/Observe requests.
+* Improved feature flag to prevent removal of default query with `null` label. This allows the default query to be used in conjunction with feature flags.
+