Feature: Add validation conditions on input variables

[benoit-garcia]

To make the module more reliable, we should set validation condition on input variables:

• cluster_version is a supported version (would require to maintain the list of supported version)
• instance_type is correct (would require to maintain the list of available instances)
• network_acl and service_ips are correct IP addresses
• private_network and project_id are UUIDs (with or without a zone prefix)
• user_name won't be rejected by redis.
• user_password matches complexity rules set by Scaleway.
• zone matches a known zone (would require to maintain the list of available zones)
• ...