Using force_alphabetical_sort_within_sections to disable case sensitive sort order within sections

Summary:
Meta:
Why are we making this change?
To match the convention of other codebases in Meta.
Reference:
https://fb.workplace.com/groups/pyfmt/posts/925830131387837/
D35553814 (facebookresearch@7d6a682)

Why are we not moving to usort yet?
1. We have other customizations in ./dev/.isort.cfg like
2. usort does not seem to be installed by default on the on-demand instances.

Reviewed By: mannatsingh, sdebnathusc

Differential Revision: D35629371

fbshipit-source-id: 6aae7bc9fd20f139ff5bb5ed9a5f30a961b77cb9

Author: Vaibhav Aggarwal

dev/.isort.cfg

@@ -7,3 +7,6 @@ default_section = THIRDPARTY
 lines_after_imports = 2
 combine_as_imports = True
 skip=pycls/datasets/data
+# Using force_alphabetical_sort_within_sections to match other Meta codebase
+# convention.
+force_alphabetical_sort_within_sections = True