Add support for creating SLA domains

[DamaniN]

Add the ability to create SLA domains for all workloads. The first revision should support creating SLA domains for all AWS and Azure snappables. SLA domain creation needs to include configuring archiving and replication.

[pl-andykalman]

I heavily support this idea that @DamaniN proposes as well. Right now, we are using the CNP module and accounts are onboarded with no SLA domain. This makes the automation fractured. I'd propose the following resources & data sources as starters. Also related to #134 .

Data Sources:
polaris_sla_domain

Resources:
polaris_sla_domain
polaris_sla_domain_assignment

More forward thinking, has there been any consideration to an OU type of construct for cloud accounts? Similar to AWS Organization OUs or Azure Management Groups where these are targets for policy attachments that inherit down. Would be nice to be able to attach SLA domains to something like this and have accounts inherit. Thanks!