housekeeping: allow overriding `swagger-ui-react` version` (via #5300)

...by setting the `REACT_FLAVOR_VERSION_IDENTIFIER` env var

flavors/swagger-ui-react/release/create-manifest.js

@@ -2,4 +2,8 @@ var jsonMerger = require("json-merger")
 var fs = require("fs")
 var result = jsonMerger.mergeFiles(["../../../package.json", "template.json"])
 
-process.stdout.write(JSON.stringify(result, null, 2))
\ No newline at end of file
+if(process.env.REACT_FLAVOR_VERSION_IDENTIFIER) {
+  result.version = process.env.REACT_FLAVOR_VERSION_IDENTIFIER
+}
+
+process.stdout.write(JSON.stringify(result, null, 2))