az storage blob upload - support for standard base16 (hex) md5sum

As good as nobody in the world uses base64 encoded md5sums and most people would not even know how to generate it from a normal base16 encoded md5sum.

Please support both. If overhead is of concern consider compression. JSON is a large overhead format so the extra "compression" of base64 should be irrelevant here vis. user workflows.

```
trainer:/workdir/eee# az storage blob upload -c models --file model.onnx --name p11808/model.onnx --overwrite=true --content-md5 aba1a2322a80eee3b400679c8a50986b
Argument '--overwrite' is in preview and under development. Reference and support levels: https://aka.ms/CLI_refstatus
Finished[#############################################################] 100.0000%
The MD5 value specified in the request is invalid. MD5 value must be 128 bits and base64 encoded.
RequestId:208740f5-301e-008b-07b2-1e6451000000
Time:2023-01-02T13:57:18.5449066Z
ErrorCode:InvalidMd5
trainer:/workdir/eee#
```