Add ews to AuthProvider enum (#240)

Add EWS to list of supported providers. This value is used for on-prem
exchange grants in v3.

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Co-authored-by: Nick Bair <[email protected]>

src/main/kotlin/com/nylas/models/AuthProvider.kt

@@ -20,4 +20,7 @@ enum class AuthProvider(val value: String) {
 
   @Json(name = "icloud")
   ICLOUD("icloud"),
+
+  @Json(name = "ews")
+  EWS("ews"),
 }