GH-35531: [Python] C Data Interface PyCapsule Protocol (#37797)

### Rationale for this change

### What changes are included in this PR?

* A new specification for Arrow PyCapsules and related dunder methods
* Implementing the dunder methods for `DataType`, `Field`, `Schema`, `Array`, `RecordBatch`, `Table`, and `RecordBatchReader`.

### Are these changes tested?

Yes, I've added various roundtrip tests for each of the types.

### Are there any user-facing changes?

This introduces some new APIs and documents them.

* Closes: #34031
* Closes: #35531

Authored-by: Joris Van den Bossche <[email protected]>
Signed-off-by: Antoine Pitrou <[email protected]>

Author: wjones127

docs/source/format/CDataInterface.rst

@@ -990,3 +990,14 @@ adaptation cost.
 
 
 .. _Python buffer protocol: https://www.python.org/dev/peps/pep-3118/
+
+Language-specific protocols
+===========================
+
+Some languages may define additional protocols on top of the Arrow C data
+interface.
+
+.. toctree::
+   :maxdepth: 1
+
+   CDataInterface/PyCapsuleInterface