PEP 766: Explicit Priority Choices Among Multiple Indexes (index priority) (#4123)

* add index priority pep draft

* Address feedback from Barry and Ethan

* PEP 766: explicit priority choices among multiple indexes

Apply suggestions from code review

Co-authored-by: Hugo van Kemenade <1324225+hugovk@users.noreply.github.com>

* address feedback from DPO and linting

* revise text

* Apply suggestions from code review

Thanks Hugo!

Co-authored-by: Hugo van Kemenade <1324225+hugovk@users.noreply.github.com>

---------

Co-authored-by: Hugo van Kemenade <1324225+hugovk@users.noreply.github.com>

Author: msarahan

.github/CODEOWNERS

@@ -642,6 +642,7 @@ peps/pep-0761.rst  @sethmlarson @hugovk
 peps/pep-0762.rst  @pablogsal @ambv @lysnikolaou @emilyemorehouse
 peps/pep-0763.rst  @dstufft
 peps/pep-0765.rst  @iritkatriel @ncoghlan
+peps/pep-0766.rst  @warsaw
 # ...
 peps/pep-0777.rst  @warsaw
 # ...