[docs] add StepLauncher supersession notes (#25335)

## Summary & Motivation

`StepLauncher` is being superseded by Pipes. 

I added `@deprecated` to all relevant objects. 

Should [this](https://docs.dagster.io/integrations/spark#submitting-pyspark-jobs-on-emr) section now point to `PipesEMRClient`? It's kinda ready but not fully tested yet. 

## Changelog

Step Launchers are superseded by Dagster Pipes and will no longer be developed. Learn more here: <future-github-discussion>

docs/sphinx/sections/api/apidocs/internals.rst

@@ -214,8 +214,8 @@ Exception handling
 
 ----
 
-Step Launchers (Experimental)
------------------------------
+Step Launchers (Superseded)
+---------------------------
 
 .. currentmodule:: dagster
 

python_modules/dagster/dagster/_core/definitions/step_launcher.py

@@ -2,6 +2,7 @@
 from typing import TYPE_CHECKING, Iterator, Mapping, NamedTuple, Optional
 
 import dagster._check as check
+from dagster._annotations import superseded
 from dagster._core.definitions.reconstruct import ReconstructableJob
 from dagster._core.execution.retries import RetryMode
 from dagster._core.storage.dagster_run import DagsterRun
@@ -56,6 +57,13 @@ def __new__(
         )
 
 
+_step_launcher_supersession = superseded(
+    subject="StepLauncher",
+    additional_warn_text="Consider using Dagster Pipes instead. Learn more here: https://docs.dagster.io/concepts/dagster-pipes",
+)
+
+
+@_step_launcher_supersession
 class StepLauncher(ABC):
     """A StepLauncher is responsible for executing steps, either in-process or in an external process."""
 

python_modules/libraries/dagster-aws/dagster_aws/emr/pyspark_step_launcher.py

@@ -13,7 +13,7 @@
     resource,
 )
 from dagster._core.definitions.resource_definition import dagster_maintained_resource
-from dagster._core.definitions.step_launcher import StepLauncher
+from dagster._core.definitions.step_launcher import StepLauncher, _step_launcher_supersession
 from dagster._core.errors import DagsterInvariantViolationError, raise_execution_interrupts
 from dagster._core.execution.plan.external_step import (
     PICKLED_EVENTS_FILE_NAME,
@@ -147,6 +147,7 @@
         ),
     }
 )
+@_step_launcher_supersession
 def emr_pyspark_step_launcher(context):
     # Resolve legacy arguments
     if context.resource_config.get("local_job_package_path") and context.resource_config.get(
@@ -216,6 +217,7 @@ def emr_pyspark_step_launcher(context):
 )
 
 
+@_step_launcher_supersession
 class EmrPySparkStepLauncher(StepLauncher):
     def __init__(
         self,

python_modules/libraries/dagster-databricks/dagster_databricks/databricks_pyspark_step_launcher.py

@@ -19,7 +19,11 @@
 )
 from dagster._core.definitions.metadata import MetadataValue, RawMetadataValue
 from dagster._core.definitions.resource_definition import dagster_maintained_resource
-from dagster._core.definitions.step_launcher import StepLauncher, StepRunRef
+from dagster._core.definitions.step_launcher import (
+    StepLauncher,
+    StepRunRef,
+    _step_launcher_supersession,
+)
 from dagster._core.errors import DagsterInvariantViolationError, raise_execution_interrupts
 from dagster._core.events import DagsterEvent, DagsterEventType, EngineEventData
 from dagster._core.events.log import EventLogEntry
@@ -169,6 +173,7 @@
         ),
     }
 )
+@_step_launcher_supersession
 def databricks_pyspark_step_launcher(
     context: InitResourceContext,
 ) -> "DatabricksPySparkStepLauncher":
@@ -188,6 +193,7 @@ def databricks_pyspark_step_launcher(
     return DatabricksPySparkStepLauncher(**context.resource_config)
 
 
+@_step_launcher_supersession
 class DatabricksPySparkStepLauncher(StepLauncher):
     def __init__(
         self,