[core] plugins: Add backbone for RezProcessEnv

The command's prefix and suffix are correctly set, but Meshroom still
needs to be injected to the list of rez packages in order to be available
in the `PYTHONPATH`.

meshroom/core/plugins.py

@@ -114,6 +114,31 @@ class DirTreeProcessEnv(ProcessEnv):
         return super().getCommandPrefix()
 
 
+class RezProcessEnv(ProcessEnv):
+    """
+    """
+    def __init__(self, folder: str, envType: ProcessEnvType = ProcessEnvType.REZ, uri: str = ""):
+        super().__init__(folder, envType)
+
+        if envType != ProcessEnvType.REZ:
+            raise RuntimeError("Wrong process environment type.")
+        if not uri:
+            raise RuntimeError("Wrong URI for Rez environment process.")
+
+    def getEnvDict(self):
+        env = os.environ.copy()
+
+        return env
+
+    def getCommandPrefix(self):
+        if Path(self.uri).exists() and Path(self.uri).suffix == ".rxt":
+            return f"rez env -i {self.uri} -c '"
+        return f"rez env {self.uri} -c '"
+
+    def getCommandSuffix(self):
+        return "'"
+
+
 class NodePluginStatus(Enum):
     """
     Loading status for NodePlugin objects.