Blobstore clients supports PUT headers

[mvach]

What is this change about?

When putting blobs via signed urls to Azure Blobstore, then the mandatory header 'x-ms-blob-type' has to be set to value 'blockblob'. Therefore we add a mechanism to support PUT headers.

We are doing it just the same why like encryption headers can be set for GCS.

[mvach]

Hi @jpalermo,
we did not test this PR right now but just want to double check if the approach is right from you perspective.
So you feedback is very welcome :-)

[jpalermo]

I haven't looked at it super closely, but I wonder if we can just combine all the headers in the blobstore client classes and rename signed_url_encryption_header to just signed_url_headers and let the blobstore object determine which headers should be included.

[mvach]

Hi @jpalermo,
Thx for the feedback, I fully agree but just wanted to follow the existing implementation, even if I wondered about these outside existences checks.
I'll update the PR accordingly.

[mvach]

After incorporating the feedback we started validating the PR in our local test environment.

[mvach]

We successfully finished testing this PR on our azure landscape.

[mvach]

Hi @jpalermo, hi @aramprice,
a review would be very nice.

[mvach]

Hi @aramprice,
if you are fine with the PR, then an approval would be nice.

[jpalermo]

👍