Add a support for write-only argument for bitbucket_deployment_variable

[ghost]

I am using bitbucket_deployment_variable for storing sensitive value (ie. Specific private SSH key) and I would like to manage those in terraform, using ephmeral resource.

Sadly, it's not working with bitbucket_deployment_variable because value is not a read-only argument.

I am searching for some workaround for this (typically, storing this value in another resource beore hand) but it would be nice if I could use it directly with bitbucket_deployment_variable