Add Promise Support for transformRequest

[WatchfulEyeOfZod]

The ability to override the request to the backend is very powerful, however, it currently does not allow the use of async/await which is required for overriding some calls to the back end.

I am currently working on supporting a serverless AWSnLambda / AWS S3 backend for this and one when attempting to upload files, I need to make a request to the lambda to get a tempoary signedURL to use as an upload target. However, because this method does not support async, there is no way to do this . For example:

const request = {
        baseUrl: "https://my-lambda-url-in-aws/backend",
        transformRequest: req => {
            if(req.params?.q === "upload") {
                // Go Get a Temporary S3_signed_url from the backend Lambda
                // Does not work because this function does not support async
                // const result = await getUploadURL(req.params.path)
                // req.url = result.url
                // req.method = 'post'
                // req.body = result.fields
            } 
            return req;
        },
    }     

The solution (I think) would be to adjust ajax.js (here

vuefinder/src/utils/ajax.js

Line 129 in 9412224

const transformResult = config.transformRequest({

) and make this method await and accept a promise result before continuing...

Thanks! Great work on the vuefinder. This is a much needed component.