Add the dependencies to GCS, S3 and Azure Storage with extras_require

[yu-iskw]

@mouradmourafiq

Overview

I put the extra dependencies to GCS, S3 and Azure Storage, since extras_require enables us to controll the installation to keep it lightweight.

Comments

I haven't made sure if the modified client works or not with google cloud storage, s3 and azure storage yet. When I have time, I would like to do that with GCS. But since I am not a sophisticated AWS and Azure user, I won't be able to test it.

Besides, can you guide me if it has to depends on specific versions of the modules respectively?
For instance,

...
   'gcs': ['google-cloud-storage>=1.13.0'],
...

Issue

polyaxon/polyaxon#352

[mmourafiq]

I think that we can keep it as it is now, if someone reports a bug related to a specific version, we can then either set stronger dependencies or make the package compatible.

[mmourafiq]

I will merge as soon as you let me know that you have tested that the change works with GCS.

I will test the usage with Azure and S3, and possibly CGS, if I manage to test it before, I will merge the PR as well.

Thanks.

[mmourafiq]

Tried it both on azure and gcs, will try S3 later, but looks good, in any case, it's not a blocker, users can always pip install what they want.

Thanks and Sorry for late merge.

[yu-iskw]

Sorry for the delay of making sure of it. And thank you for merging it.