custom query params

[WBSemple]

This allows a map of additional query params to be passed in the options map to aws-simple-sign.core/generate-presigned-url.

My use case for this is explicitly telling s3 which content-type to put in the response headers, though I've kept it generic in case there are others.

[jacobemcken]

Thanks for taking the time to create a PR 🙏

Have you thought about or explored the potential consequences of allowing the addition of any query parameter?
And not only the following, which seem to be limited to what S3 understands:

• response-cache-control
• response-content-disposition
• response-content-encoding
• response-content-language
• response-content-type
• response-expires

Source: https://docs.aws.amazon.com/AmazonS3/latest/API/API_GetObject.html

I will need a bit of time to think about whether I will recommend specific keywords for the supported query params (currently) supported by S3 (kinda like the expires and method options), or include any param for signing (which might be unnecessary).

Maybe S3 only needs the above query params to be signed and will ignore any other 🤷
I will need to look into this.