Add option to disable ssl verification on datahub client construction

[inancdokurel]

Currently, if I try to access a GMS instance that is served under a self-signed certificate, I receive [SSL: CERTIFICATE_VERIFY_FAILED] while trying to access GMS with the client that is created. To do quick and dirty checks, providing the certificate is unnecessary.

Being able to disable ssl verification is already possible while creating a DatahubClient. I think adding the option to be able to disable ssl verification would be useful.

I already created a PR for this, #51