Update schema and create/update Environments domain methods to enforce environment name uniqueness within an application context.

atst/models/environment.py

@@ -1,4 +1,4 @@
-from sqlalchemy import Column, ForeignKey, String, TIMESTAMP
+from sqlalchemy import Column, ForeignKey, String, TIMESTAMP, UniqueConstraint
 from sqlalchemy.orm import relationship
 from sqlalchemy.dialects.postgresql import JSONB
 from enum import Enum
@@ -38,6 +38,12 @@ class Environment(
         primaryjoin="and_(EnvironmentRole.environment_id == Environment.id, EnvironmentRole.deleted == False)",
     )
 
+    __table_args__ = (
+        UniqueConstraint(
+            "name", "application_id", name="environments_name_application_id_key"
+        ),
+    )
+
     class ProvisioningStatus(Enum):
         PENDING = "pending"
         COMPLETED = "completed"