Add device-collection and workloads (#13)

CHANGELOG.md

docs/data-sources/agent_configuration.md

docs/data-sources/attestation_authority.md

docs/data-sources/collection.md

docs/data-sources/collection_instance.md

docs/data-sources/endpoint_configuration.md

docs/data-sources/managed_configuration.md

docs/data-sources/provisioner.md

docs/resources/agent_configuration.md

docs/resources/attestation_authority.md

docs/resources/collection.md

docs/resources/collection_instance.md

docs/resources/device_collection.md

docs/resources/managed_configuration.md

docs/resources/provisioner.md

docs/resources/workload.md

e2e/managed.tf

e2e/output.tf

...data-sources/smallstep_agent_configuration/data-source.tf

...a-sources/smallstep_endpoint_configuration/data-source.tf