ESPhttpUpdate.update support for x-amz-meta-s3-MD5 header in addition to x-MD5

Hi there,

im using Amazon AWS S3 to host the bin file for the http ota update. S3 is a simple http fileserver meant for hosting files. (Amazon S3 provides storage through web services interfaces). Im working on an approach which requires ESPhttpUpdate.update to call s3 directly for the update binary.


However, im getting `HTTP_UPDATE_FAILD Error (-106): Verify bin header failed` error. Because im not sending the x-MD5 header.

I did some research and unfortunately custom headers such as `x-MD5` are not supported, however, fortunately s3 does support custom headers with the pattern `x-amz-meta-*` and a value to files served by s3.



I am not a cpp dev. Ive mocked up some code, i hope someone can help me test and merge this.

[https://github.com/esp8266/Arduino/commit/95c8152d26ae245ba89d27272852722e872e831c](https://github.com/esp8266/Arduino/commit/95c8152d26ae245ba89d27272852722e872e831c)

Any assistance will be appreciated.

Thanks in advance.