feat(proxy datasource): JSON server configuration launch (#2791)

* feat: delegating dicom web proxy datasource

* fix: configurably allow WADO image loader to issue preflight OPTIONS request

* Added documentation and fixed up some error handling from PR review

* review comments changes

* another small code review fix

platform/docs/docs/configuration/dataSources/dicom-web-proxy.md

@@ -0,0 +1,54 @@
+---
+sidebar_position: 4
+sidebar_label: DICOMweb Proxy
+---
+
+# DICOMweb Proxy
+
+You can launch the OHIF Viewer with a url that returns a JSON file which
+contains a DICOMWeb configuration. The DICOMweb Proxy constructs a DICOMweb
+datasource and delegates subsequent requests for metadata and images to that.
+
+Usage is similar to that of the [DICOM JSON](./dicom-json.md) datasource and
+might look like
+
+`https://v3-demo.ohif.org/viewer/dicomwebproxy?url=https://ohif-dicom-json-example.s3.amazonaws.com/dicomweb.json`
+
+The url to the location of the JSON file is passed in the query
+after the `dicomwebproxy` string, which is
+`https://ohif-dicom-json-example.s3.amazonaws.com/dicomweb.json` (this json file
+does not exist at the moment of this writing).
+
+## DICOMweb JSON configuration sample
+
+The json returned by the url in this example contains a dicomweb configuration
+(see [DICOMweb](dicom-web.md)), in a "servers" object, which is then used to
+construct a dynamic DICOMweb datasource to delegate requests to. Here is an
+example configuration that might be returned using the url parameter.
+
+```json
+{
+  "servers": {
+    "dicomWeb": [
+      {
+        "name": "DCM4CHEE",
+        "wadoUriRoot": "https://server.dcmjs.org/dcm4chee-arc/aets/DCM4CHEE/wado",
+        "qidoRoot": "https://server.dcmjs.org/dcm4chee-arc/aets/DCM4CHEE/rs",
+        "wadoRoot": "https://server.dcmjs.org/dcm4chee-arc/aets/DCM4CHEE/rs",
+        "qidoSupportsIncludeField": true,
+        "supportsReject": true,
+        "imageRendering": "wadors",
+        "thumbnailRendering": "wadors",
+        "enableStudyLazyLoad": true,
+        "supportsFuzzyMatching": true,
+        "supportsWildcard": true
+      }
+    ]
+  }
+}
+```
+
+The DICOMweb Proxy expects the json returned by the url parameter it is invoked
+with to include a servers object which contains a "dicomWeb" configuration array
+as above. It will only consider the first array item in the dicomWeb
+configuration.