feat: message orm migration (#2144)

Co-authored-by: Mindy Long <mindy@letta.com>
Co-authored-by: Sarah Wooders <sarahwooders@gmail.com>
Co-authored-by: Matt Zhou <mattzh1314@gmail.com>

letta/orm/organization.py

@@ -33,6 +33,7 @@ class Organization(SqlalchemyBase):
     sandbox_environment_variables: Mapped[List["SandboxEnvironmentVariable"]] = relationship(
         "SandboxEnvironmentVariable", back_populates="organization", cascade="all, delete-orphan"
     )
+    messages: Mapped[List["Message"]] = relationship("Message", back_populates="organization", cascade="all, delete-orphan")
 
     # TODO: Map these relationships later when we actually make these models
     # below is just a suggestion