Make content_location optional

[rylev]

Fixes #1022

This is likely not the only header that is not guaranteed to be there. We should make all headers that are not part of the common response headers list optional.

[ayngling]

We are using this SDK in production (yes, we know it is unofficial, but Rust is awesome ;) ) for many customers (hundred of thousands of users in total), and was affected by the cosmos update. Microsoft helped us by rolling back our cosmos accounts to get it working again, and hence issue #1022 was created.

The long term solution is migrating to a future version of the SDK where this is not an issue, and then upgrade the accounts again. we would appreciate very much if this commit could be merged quickly!

PS: If you arrive at this issue because you are having the same issue with an error about the "content-location" header, the temporary fix is asking Azure support to roll back your cosmos account from the "Compute Gateway for SQL API" to the "legacy gateway for SQL API".

[cataggar]

Hi @ayngling, thank you for this info. Are you able to use a main commit or do you need a published crate?

[ayngling]

I would love a published crate, but in a pinch I can use a commit :)

[ayngling]

@cataggar Actually, if it is possible, a published crate would be much appreciated!