[distributed] add PG APIs and general doc cleanups (pytorch#140853)

Doc updates:

* This adds documentation for the object oriented ProcessGroup APIs that are being used in torchft as well as pytorch/rfcs#71 .
* It also does some general cleanups to simplify the distributed.rst by using `:methods`.
* It adds `__init__` definitions for the Stores
* I've reordered things so the collective APIs are before the Store/PG apis

Test plan:

```
lintrunner -a
cd docs && sphinx-autobuild source build/ -j auto -WT --keep-going
```

Pull Request resolved: pytorch#140853
Approved by: https://github.com/kwen2501

Author: d4l3k

docs/source/distributed.rst

@@ -329,32 +329,6 @@ a github issue or RFC if this is a use case that's blocking you.
 
 --------------------------------------------------------------------------------
 
-Distributed Key-Value Store
----------------------------
-
-The distributed package comes with a distributed key-value store, which can be
-used to share information between processes in the group as well as to
-initialize the distributed package in
-:func:`torch.distributed.init_process_group` (by explicitly creating the store
-as an alternative to specifying ``init_method``.) There are 3 choices for
-Key-Value Stores: :class:`~torch.distributed.TCPStore`,
-:class:`~torch.distributed.FileStore`, and :class:`~torch.distributed.HashStore`.
-
-.. autoclass:: Store
-.. autoclass:: TCPStore
-.. autoclass:: HashStore
-.. autoclass:: FileStore
-.. autoclass:: PrefixStore
-
-.. autofunction:: torch.distributed.Store.set
-.. autofunction:: torch.distributed.Store.get
-.. autofunction:: torch.distributed.Store.add
-.. autofunction:: torch.distributed.Store.compare_set
-.. autofunction:: torch.distributed.Store.wait
-.. autofunction:: torch.distributed.Store.num_keys
-.. autofunction:: torch.distributed.Store.delete_key
-.. autofunction:: torch.distributed.Store.set_timeout
-
 Groups
 ------
 
@@ -386,6 +360,7 @@ distributed process group easily. :func:`~torch.distributed.device_mesh.init_dev
 used to create new DeviceMesh, with a mesh shape describing the device topology.
 
 .. autoclass:: torch.distributed.device_mesh.DeviceMesh
+    :members:
 
 Point-to-point communication
 ----------------------------
@@ -506,6 +481,7 @@ Collective functions
 .. autofunction:: monitored_barrier
 
 .. autoclass:: Work
+    :members:
 
 .. autoclass:: ReduceOp
 
@@ -516,6 +492,39 @@ Collective functions
 
     :class:`~torch.distributed.ReduceOp` is recommended to use instead.
 
+
+Distributed Key-Value Store
+---------------------------
+
+The distributed package comes with a distributed key-value store, which can be
+used to share information between processes in the group as well as to
+initialize the distributed package in
+:func:`torch.distributed.init_process_group` (by explicitly creating the store
+as an alternative to specifying ``init_method``.) There are 3 choices for
+Key-Value Stores: :class:`~torch.distributed.TCPStore`,
+:class:`~torch.distributed.FileStore`, and :class:`~torch.distributed.HashStore`.
+
+.. autoclass:: Store
+    :members:
+    :special-members:
+
+.. autoclass:: TCPStore
+    :members:
+    :special-members: __init__
+
+.. autoclass:: HashStore
+    :members:
+    :special-members: __init__
+
+.. autoclass:: FileStore
+    :members:
+    :special-members: __init__
+
+.. autoclass:: PrefixStore
+    :members:
+    :special-members: __init__
+
+
 Profiling Collective Communication
 -----------------------------------------